The land being placed on the surface of our globe at a level superior to that of the ocean by which its coasts are washed, there is produced continually by atmospherical conditions, a circulation of the mass of water, which evaporating from the surface, ascends as vapour to the higher and colder regions of the air, where it is condensed into clouds. These float until the electrical condition which characterizes their peculiar molecular state being dissipated, they fall as rain, as hail or snow, and the water thus regaining the solid or liquid form, tends continually by its gravity to a lower level, until it joins the general mass of ocean, from whence it had been originally derived. The rain or snow thus falling in the interior and elevated districts of the country, forms at first rivulets, then streams, finally rivers, and the force of the descending water is capable of application to give motion to machinery: it is the source, best known and most simply applicable, of water power.
If all the water which falls upon the surface of a country, as rain, passed regularly to the sea, and that the average height through which it passed, as well as its weight, were capable of being determined, it should be a simple problem to calculate the entire mechanical force thus brought into play. But there is no country in which these data are absolutely known; with us, at least, such inquiries are but in their infancy; and
p.67although the importance of the subject will not allow me to pass from it, without endeavouring to obtain at least an approximation to its value, yet I can only discuss in a general point of view the circumstances which affect the water power of this country, and having brought forward the imperfect materials that I have been able to collect, endeavour to excite others to a sense of what still remains to be done.
It is but lately that observations of the quantity of rain that falls in Ireland have been made with accuracy over a number of points. Exposed to the first brunt of the Atlantic storms, a vast body of rain is carried to these islands by the southerly and westerly winds. In average, half as much more rain falls in England than on the Continent of Europe. Here there is probably not more actual rain than in England, but there is more damp. Long since Arthur Young noticed the difficulty of drying agricultural produce in this country, and assigned to this humidity the rapid vegetation which clothes our surface with natural herbage, even where there is scarcely a trace of soil. It is hence that this island has been called the Emerald set in the ring of the sea. The moisture of the air in Ireland is thus greater than in England, and the quantity of rain that actually falls is in average certainly not less. The results that have been obtained up to the present time, by various observers, are as follows:
In the table are given the names of the observers, the localities, and the mean quantity of rain deduced from observations of a certain number of years.
|Locality||Stated by||Quantity (In.)||Average of|
It is thus seen that Dublin is one of the dryest, and Cork one of the wettest places where observations have been made. Indeed both here and in England a vast difference exists between the quantities of rain which fall on the eastern and western coasts, but our west coast has not hitherto been in such
p.68a social condition as admits of consecutive scientific observations. There is no doubt, however, but that the amount of rain falling on the west coast equals the highest number given above (that of Cork); and we shall certainly not exceed if we value the average quantity of rain that falls over the entire surface of Ireland at thirty-six inches.
If all the rain that falls on the surface of Ireland in a year were collected, it should thus cover the island to the depth of thirty-six inches; and as the area of Ireland amounts to 20,808,271 square acres, containing 100,712,631,640 square yards, there are hence this number of cubic yards of water precipitated on the surface of Ireland every year. Of this a quantity, which we shall now seek to determine, becomes available for industrial purposes. All this mass of water does not reach the sea. The spontaneous evaporation which is carried on by every point of surface that is not absolutely dry, raises again into the atmosphere a large proportion of it. This proportion is difficult to determine, indeed impossible to determine with accuracy, it may still be approximated to in the following manner.
Mr. Dobson made experiments at Liverpool, to ascertain how much water evaporated in a year from a surface of water. The mean quantity of rain was 37.48 inches. The mean quantity of water evaporated was 36.78. Hence, if there was no dry land the rain and evaporation should balance; but the soil evaporates much less than a surface of water, and a rocky surface or dry ground scarcely evaporates at all. The illustrious Dalton carried on experiments, in conjunction with Mr. Hoyle in Manchester, on this point. He had a box filled with soil, and tried how much less rain came off from it than from a rain guage, the difference of course was due to evaporation; the rain was 33.56 inches; the evaporation was 25.16 inches. The evaporation from water was at the same time forty-four inches.
That the evaporation from a surface of water is in these islands so low as the results of Dobson and Dalton indicate, is due to the moisture of the climate; our atmosphere being already more or less loaded with vapour, and thereby preventing
p.69any further increase. This is seen in the great amount of the evaporation from a surface of water in the continental states removed from the ocean. Thus, at Mannheim the evaporation is seventy-three inches, whilst the rain is but twenty-one.
Dr. Thompson values the average evaporation from the surface of Great Britain at thirty-two inches. As the evaporation from soil is less (twenty-five by Dalton's result), and from shallow soil or rocky surface still inferior, we cannot be far from the truth in considering the quantity of rain that is not returned to the atmosphere from the surface, to be one-third of that which falls. The conclusion to which Baron Dupin arrives in discussing, for France, a question similar to that which occupies us here is ultimately the same, although some of the principles from which he calculates cannot, as I conceive, be considered as applicable to this country, as the extent of evaporation is affected to an important degree by the geographical contour of the surface, by the neighbourhood of the ocean, and by the prevailing winds.
We have, in fact, considered the evaporating surface to be as the surface receiving the rain, horizontal and equal. But in nature such does not occur. Take the instance of a valley, bounded by sloping hills, clothed with a scanty verdure. It is evident that during rain the water flows rapidly down the sides of the hills, and collecting in the valley, converts its tranquil rivulet for the time into a mountain torrent. The water is here removed from the surface of the hills before it has time to evaporate. It is accumulated under an area of probably not one-tenth of that on which it fell, and its tendency to evaporate is reduced in the same degree. That such condition is not merely the fancy of a theorist, but is considered as real by the best practical authority, is fully shewn in the admirable report on the proposed reservoirs of the Upper Bann drawn up by Mr. Fairbairn. After general observations, nearly similar to those I have now made, he says: in the case of the Deer Meadow Lake, bounded by mountains whose ridge forms a rain guage of 1802 acres, with an average height of 500 feet above the reservoir, of which the area is 215 acres. Here the basin
p.70is to the reservoir as 1802 to 215, or 8 to 1; and as there can be but little evaporation, except from the reservoir, the loss is very small in proportion with the supply. Under these circumstances he considers five-sixths of the rain that falls represents fairly the supply running into the reservoirs. We shall hereafter see that the quantity of water rendered available by those reservoirs even exceeded Mr. Fairbairn's expectations.
Without more circumstance, I shall, therefore assume, that out of the thirty-six inches of rain that annually fall in Ireland, twelve inches finally arrive at the sea, and in its course may become available to industry with a force proportional to the height through which it falls. This height requires also an approximate determination.
The great limestone plain, which occupies the central counties of Ireland, has an elevation throughout its principal extent of from 200 to 300 feet, the summit levels of the canals which traverse it, being but about 300 feet above the level of the sea. Its hilly portions may be considered as raising its total average to the height last named. As I am most anxious to avoid every source of error in excess, even at the risk of falling into the opposite extreme, I shall consider the mountainous regions of the north, the west, and south, as adding to the height of the central plain but 150 feet, and assume as the average height of the surface of Ireland 450 feet. That is to say, the water which flows in our rivers to the sea has an average fall of 150 yards, and now finally we may calculate the total water power of Ireland. We had for the total quantity of rain falling in a year 100,712,031,640 cubic yards; of this one-third flows to the sea, that is 33,237,343,880 cubic yards, or for each day of twenty-four hours, 91,061,216 cubic yards, weighing 68,467,100 tons. This weight falls from 150 yards, and as 884 tons falling twenty-four feet in twenty-four hours is a horse power, the final result is, that in average we possess distributed over the surface of Ireland a water power capable of acting night, and clay, without interruption, from the beginning to the end of the year, and estimated at the force of 3227 horse power per foot of fall, or for the entire average fall of 450 feet, amounting to 1,452,150 horse power.
But mechanical power is never thus unintermittingly driven, and if we reduce this force to the year's work of 300 working days, of twelve hours each, we find it to represent 3,533,565 horse power, that is more than three million and a half of horse power. Of course much of this enormous quantity of force exists in localities where other circumstances may prevent it becoming useful. The various water machines also incur a certain loss of force in working, which may be estimated at a third. But still it may be considered as decisively established, that there is derivable from water power, of which I have here noticed only one source, an amount of mechanical force sufficient to the development of our industry on the greatest scale.
The manner in which this force is geographically distributed may be inferred from the position of the principal rivers, the structure of the country through which they flow, and the areas of catchment basins from which, through their tributaries, they derive their supply of water.
The great central limestone district may be considered as transmitting its waters to the sea, by means of the
Shannon, whose total basin is 4544 square miles.
Barrow, Nore, and Suir, whose total basin is 3400 square miles.
And partly also by the
Galway waters (Loughs Corrib and Mask), whose basin covers, . . . 1374 square miles.
Moy, whose basin covers, . . . 1033 square miles.
Blackwater in Meath, and Boyne, whose basin covers, . . . 1086 square miles.
Liffey, Dodder, and Tolka, whose basin covers, . . . 568 square miles.
But these rivers derive a great deal of their supply from the mountainous districts of Wicklow, Tipperary, Cavan, and Connemara, by which the limestone plain is bounded.
The eastern flank of the Wicklow and Wexford mountains is drained principally by the
Slaney, from a basin of 815 square miles.
Avonmore, from a basin of 200 square miles.
Avoca River, from a basin of 281 square miles.
The southern counties of Munster supply the waters of the
p.72large rivers, which flowing in parallel valleys, east and west, discharge into the ocean on the south-eastern coast. These are:
Moreover, the littoral counties pour into the sea a large portion of their drainage waters, by means of a number of rivers of short course, and individually of trifling area of basin; of these may be taken as examples the Lagan at Belfast, draining 227 square miles; the Roughty at Kenmare, from 475 square miles; the Main and Inney at Killarney, from 511 square miles; the Feale and Gale, which unwater the south-western portion of the Munster coal district and discharge into the sea near Listowel, from a basin of 479 square miles.
Now from the consideration that in average there passes to the sea from the surface twelve inches of water, which from the entire area of Ireland, 32,513 square miles, is capable of generating 3227 horse power per foot of fall, it follows that it requires the drainage of just ten square miles to give water for an average horse power per foot of fall; and on this principle the force capable of application from the waters of the individual rivers may be estimated. Of course it will be understood, that the force of a tributary, or of the upper portions of the river itself, will not be that derivable from the total catchment basin, but from the portion of the basin which actually supplies water to the point where the power is required.
For most of the estimates of areas of drainage basins given above, I am indebted to the kindness of Mr. Mulvany, Commissioner of Drainage.
In some, though few, instances, I have obtained values for the water power of certain localities, which may give rather more special interest to the subject, after the general discussion that has just closed.
The Shannon, that great river, which, penetrating the interior of Ireland, navigable from the ocean to its source, rising in one coal formation, emptying itself through another, and washing the banks of our most fertile counties, delivers into the sea the rain collected from an area, which, according to Mr. Mulvany's estimate, embraces 3613 square miles of country, north of Killaloe. This noble river which at Lough Allen, near its source, is but 146 feet above the level of the sea, passes slowly along, falling but fifty feet in 150 miles, until it arrives at Killaloe, where its waters rush down the great rapids towards Limerick, and in a space of fifteen miles present a difference of level of ninety-seven feet, of which the available power may be estimated at least with tolerable approximation, from the returns and reports published by the Commissioners for the improvement of its navigation.
In the geographical character of the basin of the Shannon, we find all the conditions for great evaporation fulfilled. The country, whose waters it receives, is flat, its streams sluggish, the soil upon its banks either deep and retentive clays, or extensive bog. Expanding into numerous lakes of considerable size, often overflowing the lowlands on its banks, it may be considered as almost in the condition of presenting a true water evaporating surface. Still the quantity of water it carries to the sea is of extraordinary power. It has been observed that, in wet weather, the level of the water in Lough Derg often rises two or three inches in twenty-four hours; and has been known to rise twelve inches. As the area of the Lough is 30,000 statute acres; this extent of water weighs 3,000,000 tons for each inch, and hence, so much as 36,000,000 of tons have accumulated in a single day and night.
The average difference between summer and winter level of
p.74the Shannon at Killaloe, where, narrowing from Lough Derg, it reassumes the river form, is about six feet, but the total of the rises of the water during the year, are found from a discussion of the observations of three years, to be eleven feet. The rising of the waters occupied in average seventy-seven days: in falling to the summer level they occupied 107 days. The quantity of water thus accumulated in the great natural reservoir of the Lough was 532,554,096 cubic yards, or 403,416,600 tons, which is discharged in 107 days at the rate of 155,926 tons per hour. By this, a force continuous day and night of 177 horse power per foot of fall, may be produced. An equal force is of course available whilst the river is rising, and thus through 184 days, or six months of the year, this enormous power is in action, independent of the ordinary discharge which goes on when the waters are at the lowest.
When the river is high, the motive force available is far greater than that just now mentioned. An example furnished to me by Mr. Mulvany will shew this sufficiently. On the 2nd of December, 1836, when the water was 13 feet on the upper sill of Killaloe lock, the observed discharge was 882,450 cubic feet per minute, and on the 10th of that month, the height was 14 ft. 1 in., on the 18th 14 ft. 4 in., at which height it continued untill the 25th, with of course a greatly increased discharge, on the latter day it began to descend gradually. During the period mentioned, the whole lake rose four inches between the 3rd and 4th, and five inches in two days, between the 5th and 7th, and two inches in other days. These grand rises, at that height of water extended over the flooded lands as well as the lake, that is, over a surface of from 36000 to 38000 statute acres. Now the discharge for the month of December, 1836, may certainly, from the description above given, be taken at one million cubic feet per minute, that is, one and two-third million of tons of water per hour, capable of producing 1885 horse power per foot of fall.
The minimum discharge of the Shannon at Killaloe has been estimated by Mr. Mulvany, in the dryest summer, so low as 100,000 cubic feet of water per minute. This is equal to a force of 188 horse power per foot of fall. At this minimum,
p.75however, the flow is kept but for a very short time, certainly not more than a month in the year, which is also the duration that may be allotted to the maximum elevation of the waters.
Although it is not possible to deduce from these returns the actual average force exerted by the waters of this river, yet I consider from all the facts I have been able to collect, regarding its discharge at various seasons, that the mean cannot fall below 350 horse power per foot of fall. For as the summer level of the river for which the minimum discharge is taken, does not last more than two months, and that during the six months of the rising and the falling of the waters, the force is at least 188 + 177 horse power per foot of fall, and finally, that the maximum delivery at winter level, lasts at least a month, there are nine months of which the force per foot of fall are
2 months at 188, . . . 376
6 months at 365, . . . 2190
1 month at 1885, . . . 1885
Which give an average of 495 horse power. The other three months are certainly not below the six months of rising and falling, but in order that the final results may not be possibly liable to any suspicion of exaggeration, I shall take the average force of water available per foot of fall, at 350 horse power, which gives for the ninety-seven feet of fall between Killaloe and Limerick, a total of 33,950 horse power in continuous action, day and night, throughout the year.
This, however, is by no means the whole power of the river, for although in the upper portion of its course it flows through a district unusually level, there is yet between Lough Derg and Lough Allen a total available fall of forty-six feet six inches. We may consider, that at the several points on the river, the supply of water will bear the same proportion to that at Killaloe, as exists between the respective areas of their catchment basins, and this is shewn to be a very legitimate assumption, since at Carrick, where the area of basin is about 350 square miles, the minimum quantity of water passing in summer through the bridge has been determined by Mr. Mulvany to be 10,000 cubic feet per minute. This is just a tenth of the
p.76minimum at Killaloe, the basin at which is ten times the area of the surface drained at Carrick.
The distribution of the falls on the upper and middle Shannon, will be, when the improvements now in progress are completed, as follows. The area of catchment basin of the river, at each fall, and the average resulting horse power continuous is given in the accompanying column of the table.
|Area of Basin (sq miles)||Height of Fall (ft)||Total Horse Power|
|Mouth of Lough Allen||146||13||199|
The total continuous power is, therefore, 4,717 horse, which, added to that of the river from Killaloe 33,950, gives a force existing between Limerick and Lough Allen of 38,667 horse power, supposed in constant action.
The vast inequality of force at different seasons is the most remarkable disadvantage of water power. It can be perfectly and economically compensated for, as shall be seen hereafter.
To judge of the evaporation which goes on in the basin of the Shannon, we must compare those practical results with what theory indicates.
The area of the basin of the Shannon above Killaloe is 3613 square miles, and as thirty-six inches of rain give 0.3 continuous horse power per foot of fall, for every square mile of basin, the total power of the Shannon, without evaporation, should be 1084 horse power per foot of fall. Its average is found to be about 350, and hence, the Shannon transmits annually to the sea 11.6 inches of water collected from its extensive basin, a result remarkably in accordance with that of twelve inches (one-third of the rain), which I have taken as the average of Ireland.
If we pass more to the south we shall find a river in which different circumstances prevail. The Lee, rising amidst the picturesque solitudes of West Muskerry, passes by a direct and rapid course through mountainous country to Cork, where it
p.77joins the sea. I have calculated the area of country above Cork drained by the Lee at 562 square miles. The average rain should, therefore, produce 169 horse power per foot of fall. Some measurements were made at my request by a most intelligent friend, at a period when the river was very low, and admitted of greater accuracy than at other times. He found that there passed through the river in twenty-four hours, 442,800 tons of water. This is at the rate of twenty-one horse power per foot. The water passing to the sea was, therefore, just one-eighth of the rain. This was in summer. The average delivery of the River Lee is certainly more than treble this. The power calculated from the average for Ireland of one-third of the rain, should be fifty-six horse power per foot of fall. But the rain in the west of Cork is above the average; the course of the river is direct, and the slope of its basin precipitous.
A river in the north of Ireland, concerning the practical efficiency of which we possess numerical data, is the Upper Bann; it rises in Down in the Mountains of Mourne, and falls into Lough Neagh, near Lisburn. This river is the most fully economized in Ireland; its banks present a picture of industry, of comfort, and intelligence, which I am glad to hold up as a pattern to other districts. The natural supply of the river was not enough for the demands of its industrious occupiers; and Mr. Fairbairn, employed to examine how its capabilities could be increased, made a report, to which I have already had occasion to refer. I have calculated the total available catchment basin of the Upper Bann to be 256 square miles. Hence, without evaporation, and with the rain at thirty-six inches, which coincides very closely with the fact, in that locality, the horse power per foot of fall is seventy-seven. Now Mr. Fairbairn had estimated the force obtainable, when the water was fully brought into play, at eight working horse power. It has resulted, from even the partial execution of his plan, that the power is capable of increase, even beyond that, and ten working horse power per foot is what appears may be calculated on. Now this ten working horse power corresponds to fifteen horse power on the theoretical standard I have assumed,
p.78which supposes there is no loss of force, and hence the water practically available is exactly one-fifth of the rain.
Such are the few facts regarding the actual water power of certain localities which I have been able to collect. It shews how much remains to be done in this department of practical science. If it in any way indicates the route; if among my readers some may be induced by these explanations to occupy themselves, whilst in the provinces, in those operations, really simple, only requiring care, by which the sectional area and the velocity of the current in a river are determined, the country will be positively benefited; for such determinations are at the basis of all investment of capital for industrial objects, and the want of them often has occasioned considerable loss of time and money.
Before quitting this subject I may mention, that Mr. Bald has published some estimates of the water power of certain localities. He considers that eighteen inches of rain pass to the sea. This is certainly above the truth. Consequently all his numbers are too high.
Mr. Henessy, who has recently published an estimate of the total water power of Ireland, supposes, that four-fifths of the rain become available for industry. This proportion, although it may exist in certain mountainous districts, where the water collects rapidly in basins of small area, and passes with a short course to the sea, is certainly too large for an average estimate, and he has not attempted to support his views upon any definite numerical results. But Mr. Bald's measurement of the areas of the basins, and of the heights of fall of localities of water power in the west of Ireland, are very valuable, and I have from them calculated the available horse power of the Connaught lakes, which, together with the area of catchment basin, and the height of fall is given in the following table
|Lakes||Catchment Area||Fall||Horse Power|
|Conn and Cullin||900||27||2430|
|Mask and Corrib||1374||36 resp. 14||6850|
We have now sufficiently discussed the manner in which the water power of Ireland originates, its distribution, and, so far as our materials allow, its amount. We cannot, however, part from the subject without describing, though briefly, its practical application. It is not my purpose to describe the mechanical details of water engines. This is done by special mechanical writers. Some engines are fitted for some uses and for some localities, others for different conditions; and it is essential to the connexion of our subject that a certain analysis of the economic efficiency of each should be given here.
We may reduce the water engines to four classes. In the first the water acts by its weight; of this kind is the overshot water-wheel. In the second the action is by impulse, as in the undershot wheel. In the third it is by pressure, as in the water pressure machine. In the fourth, it is by reactive pressure, as in Barker's mill; and similarly reactive impulse gives origin to the horizontal wheel or turbine.
The overshot water-wheel is the most important engine of water power. It is applicable under a great variety of circumstances, and from its inertia it serves as a regulator as well as a producer of the velocity of machinery placed in connexion with it. Its construction requires considerable mechanical skill that its powers may be brought fully into play; the form of the buckets; the quantity of water let into each bucket; the point of the circumference at which the water is to be let on; the exact centreing of it, so that its motion may be absolutely uniform; all these are points to be carefully executed, as the injurious results of a fault in the prime mover might be very serious. When an overshot water-wheel is well made, and well proportioned to the supply of water, we may consider that there is absorbed by the machine one-fourth of the power of the water, and that three-fourths are delivered capable of producing useful effect. In some wheels 80 per cent. of useful effect are obtained, but this seldom occurs.
Wherever the supply of water is moderately large, and that the height of available fall lies between fifteen and fifty feet, the overshot wheel is certainly the engine to be adopted under ordinary circumstances. It is not liable to injury; it is easily
p.80repaired; and its prime cost, in relation to its power, is not considerable. In order to derive from it all its power, it must be recollected, however, that the water should act only by its weight; the principle on which its maximum action depends being, that the water should enter the wheel without impulse, and should leave it without velocity. To fulfil this condition, as far as possible, should be the object of the engineer.
In level countries, where, though the quantity of water may be large, the height of fall may be but a few feet, the undershot wheel is often employed. The water acquiring a velocity from rushing down an inclined race, strikes the float-boards near the bottom of the wheel, and communicates to the machinery a portion of its own motion. The float-boards are generally set radial; but sometimes they make an angle of 20[deg ] with the radius. In the latter case the water acts slightly by its weight; but there does not appear to be much difference in the practical results. Now this undershot wheel must be understood to be an imperfect machine. In the overshot wheel the theoretic value of the water is equal to its weight multiplied by its height of fall, and of this force three-fourths is actually available in practice. In the undershot, on the other hand, the theoretic power is but half the weight of the water multiplied by its height of fall, and of this but two-thirds are available in practice. Hence, the final performance of the undershot wheel is but one-third of the total theoretic power of the water expended. This machine should, therefore, never be used where any other is practicable: it is the least economic. Still in the level districts of Ireland numerous positions occur, where a large quantity of water falls through a height of from two to six feet. Here one-third of the power may be economized by an undershot wheel, and may suffice for all the industrial wants of that particular locality. Beyond six feet, however, I consider this machine not to be recommended. From six feet to fifteen feet of fall, the interval between the effective limiting height of water for the undershot and overshot wheels, a form of wheel intermediate to those, indeed compounded, as it were, of them, is most advantageously employed; this is the breast wheel.
The breast wheel has float boards like the undershot, but instead of moving in an open race, it revolves in a carefully constructed channel, the sides of which are so closely fitted to its frame, as with the float boards to form in some degree a set of buckets. The water is let on somewhat below the axis, and entering the channel with some velocity, it acts at once by weight and impulse. The power of the breast wheel is intermediate to those of the wheels already noticed. It is in fact compounded of the two, and in the words of Barlow: The effect of the breast wheel is equal to that of an undershot whose head is equal to the difference of level between the surface of the reservoir and the point at which it strikes the wheels, added to that of an overshot whose height is equal to the difference of level between the point where it strikes the wheels and the level of the tail water. Now this gives for the breast wheel a theoretic power of 83 per cent. of the whole effect of the water. In practice about a third of this is absorbed by the machine, and hence the available working effect of the breast wheel may be taken at 55 per cent., rather more than half of the calculated force of the water.
M. Poncelet has proposed to form the breast wheel still more on the model of the overshot, by giving to the float boards a curved form, that they may act more effectually as buckets. He considers also that the principle of the overshot should be used in letting on the water, that is, that it should enter without impulse and leave without velocity. A model wheel constructed on his plan gave a useful effect of 74 per cent. of the total power, and working wheels, of which many of large size have been erected in France, are found to economize from 70 to 60 per cent., below which none have fallen. They may be considered as giving in average two-thirds of the total power of the water, and are hence better than the breast wheels of ordinary construction.
In conclusion I add in a tabular form, the proportional available power by each kind of wheel and the heights of fall within which its use may be recommended.
|Wheel||Economy of power (per cent)||Limits of head (ft)|
|Overshot||75||15 to 50|
|Breast||55||6 to 15|
|Undershot||33||2 to 6|
|Poncelet||66||6 to 15|
A question may naturally be asked by those not practically conversant with those matters, why then ever use one of those inferior wheels if you have a fall of twelve feet? why use a breast wheel of thirty feet which economizes but two-thirds of the power, and not an overshot of fourteen feet, which might economize three-fourths. It is that there is a great practical advantage in large wheels. The motive force acts to more advantage at the extremity of a longer lever. The angular velocity becomes small, which is one of the conditions necessary to a maximum economy, and the mass of the wheel acts as a fly wheel, and by its inertia preserves a regularity of movement which is of the highest importance in practice. Hence the wheels should always be as large as the mechanical circumstances of their locality admit, and thus the practical limits above assigned are fixed.
It will be seen from the numbers now given, that the average performance of breast and overshot water wheels, taken together, is close to two-thirds of the calculated power of the water they expend. On this is founded a practical estimate of the power of mill streams, frequently employed by engineers, and which it is useful to know. It is that twelve cubic feet of water falling one foot per second is a horse power available. Now this is 720 cubic feet per minute, and as the cubic foot of water weighs 62.5 lb, the weight is 45,000 lb falling a foot per minute. This is four-thirds of the theoretic horse power as I have stated at page 42, and thus one-third additional power is assumed as expended in transference to the machines.
The water-pressure engine is a machine but little known in this country. In fact, borrowing as we do our mechanical ideas from England, a country, generally speaking, so rich in fuel, as to render the economy of water power unimportant, water engines do not fix the attention of mechanists as they deserve.
p.83In mechanism the water-pressure engine is essentially the same as a steam engine, usually single acting. The valves and passages are large, as water cannot be wire-drawn like steam. A main-pipe from a reservoir at a distance brings the water to the valve box, through which it enters the cylinder, which, raising the piston, it gradually fills: the entrance valve closes, the water is let off by the opening of an exit valve, and the piston falls by the weight of the machinery with which it is in connexion. Some engines are made double-acting, in which case they are absolutely constructed as the simple high pressure steam engine, but they use cold water in place of steam.
Now as to the mechanical power of these engines. The water acts, not by its weight or impulse, but by its pressure. The height of head to give this pressure must, therefore, be considerable, but the quantity of water consumed may be very small. In a mountainous district, a reservoir is formed among the hills. From it the water is conducted, not by a costly embankment, but by a pipe of a few inches diameter. The machine is erected at the most convenient locality. For every thirty-five feet of head, the pressure is one atmosphere on the piston, fifteen pounds to the square inch. A head of 350 feet gives, therefore, ten atmospheres, and in mining districts, where such elevation is often available, those engines are peculiarly suitable. With such a head and a piston of a square foot of surface, moving with a mean velocity of two feet per second, there should be produced a force of seventy-eight horse power, and as the engine is found to deliver in practice 70 per cent. of the theoretical amount, the working efficiency of such an engine should be fifty-four horse power. The expenditure of water would be 120 cubic feet per minute.
The expenditure of the same water, acting by the same head, on an overshot wheel, would give seventy-three theoretic horse power, and in practice fifty-five horse power. The efficiency of the water pressure engine is, therefore, a little less than that of the overshot wheel, but it is to be remarked, that a head of 320 feet could not be made use of with any wheel. A wheel cannot be practically used over fifty feet, and hence 270 feet of fall should go to waste, five-fifths of the entire
p.84power, all of which is economized with the water-pressure engine.
On the Continent the employment of water-pressure engines is very general. At Freyberg, one of the deepest silver mines, the Altemord Grube is drained by an engine working by two single acting cylinders, which is fixed itself 360 feet below the surface. Its effective duty is seventy per cent. of the calculated power. In Bavaria, where the water-pressure engine has received its most remarkable improvements, from the hands of Reichenbach, the brine, from the salt mines of the neighbourhood of Salzburg, is transmitted over the mountains, 1200 feet high, for a distance of seven miles, by means of a series of nine engines, that the evaporation may be carried on in a district where fuel is cheap. The effective duty of these engines is from 60 to 72 per cent. of the theoretical force. In France in various localities they are erected. One at Huelgoat in Finisterre, which works with a column of water, sixty-five yards high, and draws up the waters from the lead mines from a depth of 305 yards, delivers 64 per cent. of the theoretical force, and when it is placed in connexion with the deeper pits, for which it was constructed, is expected to increase its efficiency to at least 70 per cent. of theory.
These machines are now also being introduced into Cornwall. Mr. Fairbairn and Mr. Darlington have erected water-pressure engines in the mines of that country. One erected by the latter engineer has two cylinders of fifty inches diameter and ten feet stroke. It is worked by a column of water thirty inches diameter and forty-four yards high. It works four to six strokes in the minute. The blow produced by the valve is almost totally gotten rid of by peculiar mechanical arrangements invented by Mr. Darlington, but which need not be described here. The power of this machine calculated by the principles given above, from its dimensions and the supply of water, should be 166 horse power, which at 70 per cent. becomes 116 horse power of practical efficiency.
I must remark, however, two disadvantages of this machine. 1st. The water flowing with a constant pressure into the cylinder, imparts to the piston an accelerated motion, so that finally the
p.85stroke is terminated by a shock from the inelastic water, whilst in the steam engine, the steam acts as an elastic cushion, by which the piston is brought to rest, and injury to the machinery prevented. To remedy this, in the water engine, many plans are devised; an air vessel on the cylinder; springs under the working beam; a cavity containing air in the piston. By means of such provisions this disadvantage is removed, and although the motion is not regular enough for certain delicate uses, yet for draining mines and numerous other purposes it is most effectual. The second disadvantage is, that its parts, being like those of the steam engine, are somewhat complicated, and require more repair and attention than those of water wheels. But in this it is not more troublesome than the steam engine, which nobody faults on that account.
The machine which is popularly known as Barker's mill, and in which water issuing from an orifice gives motion to machinery by its reactive force, is not one with which I need occupy attention. Its theory indicates the maximum effect to be but one-half the true power of the water, and as in practice further deduction must be made, it is likely that not one-third is really economized. It is hence one of the worst water engines, and I only name it here because a modification of it by Messrs. Whitelaw and Skerrit of Glasgow has lately been brought forward, said to economize power in as great a degree as the overshot wheel. In the new form the horizontal arms are curved in such a manner, that the water when passing from the centre moves in a straight line, the arms by their curvature retracting as it advances. In this way the centrifugal force of the water, which, in the old straight arms, partly acted against the reactive force, is obviated; indeed as it is exerted along the axis of the tube, it is added to the power generated by the reaction. The results of the use of this engine published by the patentees are highly favourable to it, but I understand, that in many instances it has not fulfilled expectation. Without intending, therefore, at all to disparage this improved form of the reaction mill, I may observe that more extended practical knowledge of its power is required before we can rank it with those useful machines already noticed.
Finally I have to describe a water engine of quite modern invention and of remarkable efficiency, the Turbine, invented by M. Fourneyron. Coals being abundant the steam engine is invented in England; coals being scarce, the water-pressure engine and the turbine are invented in France. It is thus the physical condition of each country directs its mechanical genius. The turbine is a horizontal wheel furnished with curved float-boards, on which the water presses from a cylinder which is suspended over the wheel, and the base of which is divided by curved partitions, that the water may be directed in issuing, so as to produce upon the curved float-boards of the wheel its greatest effect. The best curvature to be given to the fixed partitions and to the float-boards is a delicate problem, but practically it has been completely solved. The construction of the machine is simple; its parts not liable to go out of order, and as the action of the water is by pressure, the force is under the most favourable circumstances for being utilized.
The effective economy of the turbine appears to equal that of the overshot wheel. But this economy in the turbine is accompanied by some conditions which render it peculiarly valuable. In a water wheel you cannot have great economy of power without very slow motion, and hence where high velocity is required at the working point, a train of mechanism is necessary, which causes a material loss of force. Now in the turbine, the greatest economy is accompanied by rapid motion, and hence the connected machinery may be rendered much less complex. In the turbine also a change in the height of the head of water alters only the power of the machine in that proportion, but the whole quantity of water is economized to the same degree. Thus if a turbine be working with a force of ten horses, and that its supply of water be suddenly doubled, it becomes of twenty horse power; if the supply be reduced to one-half, it still works five horse power: whilst such sudden and extreme changes would altogether disarrange water wheels, which can only be constructed for the minimum and allow the overplus to go to waste.
Mr. Rühlmann who has published a very full report on the
p.87theory of this machine, and on the practical performance of the more important of those erected on the Continent, concludes, that it is certainly wrong to suppose that turbines can altogether do away with the use of vertical wheels, and that the economy of 80 per cent. of the theoretical effect, obtained by Fourneyron with some wheels, cannot be expected in all cases, but that certainly in practice from 60 to 70 per cent. may be depended on. As to the choice between turbines and vertical wheels, his decision is, that where there is a fall of a certain height, which may be economized by means of an overshot wheel, such is to be preferred to the turbine, for when carefully arranged, the overshot wheel economizes more than 70 per cent. of the theoretical power; the only exception to this may be in those cases, where, as in corn mills, the horizontal motion of the turbine may be directly utilized, or where the engine must work against considerable backwater, in which case the effect of the turbine is but very little affected, though the ordinary wheel loses considerably in power.
But in all cases of very high or of very low falls, Mr. Rühlmann, as well as all other engineers who have written on the subject, gives decided preference to the turbine, and considers, that their universal application to such circumstances can only be retarded by want of foresight and of knowledge of their actual performance.
The extreme conditions under which the turbine will act, are shewn very satisfactorily by the result of one erected at St. Blasien, and by which is driven the machinery of a cotton mill, containing 8000 spindles, with carding machines, beaters, and all other necessary engines. The flow of water was one cubic foot per second, but a height of 332 feet was available. On a fifty foot overshot wheel, this quantity of water would give but five and three-fourths theoretical, and but four and one-fourth practical horse power; but the water, being collected at a distance of two miles, is brought to St. Blasien by a metal pipe eighteen inches diameter, and delivered to the turbine with all its pressure available. The wheel of the turbine is but one foot diameter, and it makes about 2250 revolutions in a minute. Its theoretical force is thirty-eight horse power, of which
p.88nearly three-fourths or twenty-eight horse power is delivered in practice.
Contrasted with this machine, are the great turbines erected at St. Maur, near Paris, to grind corn. The wheel of each turbine is six feet in diameter; its paddles ten inches high. The head of water averages 11 ft. 9 in., and the discharge is thirty-four cubic feet per second. Each turbine drives ten pair of millstones, with all accompanying cleansing machinery, and in twenty-four hours grinds fifteen tons of corn. The theoretical power of each turbine equals forty-five and a half horse power; the practical efficiency is thirty-three. In another case where the height of the fall of water to a turbine was but thirteen inches, the economy in practice was fifty-five per cent. of the theoretical power.
Having thus considered the machines by which water power is rendered available to industry, it remains to examine some circumstances affecting it, which are not of inferior importance.
The worst feature of water power is, that its production does not depend upon the will of the person who employs it. Originating in cosmical laws, which, from their complexity, have as yet totally defied the predicting power of science, the amount of water flowing along any given river cannot be estimated for any time in advance, and hence the manufacturer has open to him one or other of but two courses, each of which is beset with disadvantages, which I shall endeavour to enumerate. In the first place, having estimated the smallest quantity of water that is available in summer, he may proportion his machinery, and work to that amount of power. But by doing so, he sees pass by him through the greater portion of the year, power many times as great as that which he economizes. The forces of nature flow by his door, but he knows not how to control them. The powers which could execute in a day that which occupies his factory for a week, are running to waste, but the intelligence which might arrest them in their course, and make them pay tribute, is not possessed by the manufacturer whose case we have taken, and hence he drags along an existence dull and unprofitable, until some turn
p.89of commercial circumstances seals his ruin. The alternative course by which the machinery is constructed of power sufficient for the employment of the average quantity of water, is accompanied by not less evils. In fact, in the dry season, industry is arrested; there is not water enough to work the mill: workmen unemployed, their families possibly without food, a prey to discontent, are consequences sufficiently serious; whilst orders remaining unexecuted, contracts unfulfilled, may entail loss of the most serious kind upon those whose capital is invested in such works. In addition we must consider, that upon a river, factories, by which its water is economized, present great obstacles to the flowing of the current, and hence in case of sudden floods, by the arresting of the stream at the mill works, the lands higher up are rendered liable to inundations, which may be destructive to property and even life. Thus the employment of water power is liable to interruption, and may be productive of injury, affecting not merely the interests of the workmen and the capitalists who share in its advantages, but also of those at a distance who derive no benefit from its use.
I believe that the disadvantages to which water power is liable, are fully expressed in the above statement. Now I do not hesitate to say, that they are all capable of being removed. If we give to the conditions of water power, the same care that is bestowed upon the circumstances of steam power, those disadvantages disappear, and we obtain from water, during the year, a steadiness of supply, and a regularity in work that leave nothing to be desired.
In fact, as we have under the earth vast deposits of coal, the source of steam power, from which we draw, at desire, the necessary supply, so is it necessary to organize on the surface vast depositories of water power to be made available at our will. In place of wretched mill ponds, by which a stock of water is scarcely secured for a week, there should be a basin so capacious, that the floods of an entire winter might be received, and thus invested for most profitable expenditure in summer. This is the course actually pursued where industry is most active and enlightened. I shall proceed
p.90to detail the circumstances of one or two such cases, in order that they may serve as examples of what may be done.
The quantity of mechanical force that is brought suddenly into existence by the waters of a winter flood, and which, for want of sufficient reservoirs, is altogether lost in almost every case, may be exemplified by considering the quantity of water, which during a few days of the winter of 1840, accumulated in Lough Derg. The depth of water on the upper sill of Killaloe lock on the respective dates were:
|15 Nov 1840||9 ft 8½in.|
|16 Nov 1840||9 ft 9 in.|
|17 Nov 1840||10 ft 9 in.|
|18 Nov 1840||11 ft 1 in.|
|Stationary until 8 Dec 1840||10 ft 9 in.|
|9 Dec 1840||11 ft 0 in.|
|10 Dec 1840||11 ft 6 in.|
|11 Dec 1840||11 ft 11 in.|
In the twenty-four hours of the 16th and 17th November, the water rose twelve inches, and in the three days and nights of December, 8th to the 11th, it rose fourteen inches. Now each inch of water on this lake amounts to 3,000,000 of tons in weight. These floods, therefore, brought down, first in one day, 36,000,000, and then in three days, 42,000,000 of tons of water, over and above the vast discharge constantly going on at the orifice of the lake. Now if these masses of water could have been, by suitable engineering arrangements, preserved from immediate and useless expenditure; if their discharge could have been spread over the entire year, these two quantities alone, of twelve and fourteen inches of rise of surface, the fruits of four days and nights of winter flood, would be able to generate, on the fall of the river below Killaloe, a force acting throughout the entire year, night and day, of 967 horse power.
The mill owners on the Upper Bann were exposed to all the disadvantages above stated. Floods drowning their mills in winter, drought stopping their works in summer. Mr. Fairbairn
p.91was employed to survey the district, and proposed the formation of three reservoirs, the circumstances of which I shall briefly describe in his own words.
Lough Island Reavy, which is the best situated reservoir, is a natural lake bounded north and south by land of considerable elevation. It has good feeders, which, with the overplus waters of the River Muddock, would give ample supplies, and fill the reservoir once or twice in the year. The present area of the Lough is ninety-two and a half statute acres. On this is to be raised thirty-five feet of water, and drawn to a depth of forty feet under that height. The area thus enlarged will be 253 acres, equal to 140 acres thirty-five feet deep, and 113 acres fifteen feet deep, making a total of 287,278,200 cubic feet of water.
The Deer's Meadow, embanked to 100 feet above the level of the river, will flood 215 acres to twenty-four feet average depth, having 224,769,600 cubic feet of water. The feeders are uncertain, being but the drainage of 1802 acres. This reservoir should, therefore, be the last executed.
Corbet Lough is a valuable auxiliary to the other two. It has excellent feeders, and controls every mill from its outlet to Lough Neagh. It may be raised eighteen feet above its summer level. It should then cover seventy-four and a half acres, and contain 46,783,440 cubic feet of water. The supply is from the flood waters of the Bann by a canal cut and land feeders.
The sum of the three reservoirs:
cubic feet Acres covering Lough Island Reavy 287,278,200 253 Deer's Meadow 224,769,600 215 Corbet Lough 46,783,440 74 1/4 Cubic feet of water 558,831,440 542 1/4
This total amount, at sixty cubic feet per second, will afford a constant discharge for 108 days, or for 216 days, working twelve hours; and as twelve cubic feet per second falling a foot, is a working horse power, the reservoirs alone
p.92give five horse power per foot of fall for 216 days in the year. Now as there are 350 feet fall, this is a total on the Bann, of 1750 horse power, and, adding the water of the river course, the power may be considered as equivalent to 2800 horse power.
The above is extracted from Mr. Fairbairn's report; he proceeds to some estimates of the cost of these reservoirs. The total expenditure he values at £32,000, and deduces, that the annual cost of delivery of water should be £1860, arranged as below and that each reservoir gives for a shilling expense, the following number of tons of water:
|Locality||Total expense||Gives for a shilling|
|Lough Island Reavy||£700||33 tons water|
|Corbet Lough||£260||12 tons water|
|Deer's Meadow||£900||14 tons water|
Mr. Fairbairn calculates that steam power to do the same work should cost £9050, and hence the water power should produce a saving of £7191 per annum.
Such was Mr. Fairbairn's plan; I was aware that it had not been all carried into execution, but that such parts of it as were carried out had produced even greater effects than he had estimated. Through the kindness of Mr. Bergin I was enabled to communicate with Mr. Bateman, who was Mr. Fairbairn's colleague in the execution of the works, and received from him, in answer to certain queries, replies which I subjoin.
Of the works authorized by Act of Parliament, the Lough Island Reavy Reservoir has been completed, and been in operation for upwards of three years.
The land for Corbet Lough Reservoir is purchased, and the Deer's Meadow Reservoir abandoned.
Previous to the construction of the Lough Island Reavy Reservoir, the River Bann, where most closely occupied by mills and bleach works, had not water power more than equal to one or one and one-half horse power upon each foot of fall during the dry periods of the year for months together.
The lowest power now is about five horse power to a foot of fall, being a gain, by means of the reservoir, of about three
p.93and one-half horse power per foot, and the regular full quantity is uniformly maintained.
Should the Corbet Lough Reservoir ever be completed, the minimum power of the river, below its outlet, will be brought up to about ten horse power per foot of fall.
In dry seasons, when the river has fallen to its lowest volume, the discharge may probably be equal to from seventy to one hundred cubic feet per second. In floods to 3 or 4000 cubic feet per second.
Below the Lough Island Reavy Reservoir there is a fall of 124 feet upon the River Muddock, partially occupied by small corn and flax mills.
On the River Bann, from its junction with the Muddock to the Corbet Lough Reservoir, there is a fall of forty-four feet and a half, at present occupied by limited establishments, which are capable of great improvement. The regular power now is never less than about five horse power per foot of fall.
Below Corbet Lough to the last mill on the river there is a fall of 168 feet; on this portion the more extensive establishments are situated,the whole fall being occupied. The river is now equal to about five horse power per foot of fall, and by an outlay of between 2 and £3000 on Corbet Lough may be increased to ten horse power per foot.
The mills have been gradually increasing since the improvement of the river, but few are yet enlarged to the extent they may be.
The annual rate levied upon the river for the cost of the improvement is £10 per foot of fall, which will diminish as the works increase in value, and the river is more extensively occupied. As the measure of a river, when no other assistant power can be applied, must be taken at its minimum, the gain already acquired is about three and one-half horse power per foot, which, at the present rate, is equal to a cost per horse power per annum of under £3. The cost of the same power by steam in that district would be from £20 to £30 per annum.
Should the full scheme be developed by the completion of the Corbet Lough Reservoir, the cost of the additional power will be little more than 20s. per horse power per annum.J. F. Bateman.
We here see how fully the so called natural disadvantages of water power are obviated. I shall in addition notice an instance taken from Scotland, where the result has been, not merely the increase in amount and steadiness of power previously existing, but absolutely the creation of a vast water power, where none had been deemed to exist before.
The inhabitants of Greenock had long suffered from a want of water for domestic use. Several engineers had reported, that the circumstances of the locality did not allow of any copious supply of this necessary element of cleanliness and health; but at last Mr. Thorn, having examined the surrounding country, astonished the people of Greenock by asserting, that not merely water sufficient for domestic and municipal purposes might be brought in, but that water power might be made available for mechanical purposes to a very considerable amount. His scheme has been carried into effect. His calculations have been more than borne out, and the rapid rise of Greenock as an emporium of commerce and of industry is, in no small degree, due to the bold foresight of the engineer of the Shaw's water works.
I shall extract a few notices of these works from an account of them printed some years since, and now extremely rare.
The distinguishing characteristics of this scheme are the following:Instead of erecting works on natural waterfalls, on the banks of rivers, in remote and almost inaccessible places, where immense capital must, in the first instance, be expended in forming roads and houses for the work people, as well as a heavy and perpetual charge for carriage to and from the seat of trade,the water is carried, by an aqueduct, from the river and reservoirs, to a populous sea-port town, with a redundant unemployed population, where roads, harbours, piers, and every thing requisite for the most extensive trade and manufacture, are already formed. Besides, by thus forming artificial waterfalls on advantageous grounds, every inch of fall, from the river or reservoir to the sea, is rendered available; whereas, by the former mode, only a very small part of the fall could, in general, be employed. In the present case a fall of 512 feet has been made available, of which not more than twenty was formerly occupied, or thought capable of being usefully employed.
p.95But, besides the immense advantage thus gained by increasing the fall, a still greater advantage is obtained from the greatly increased, and perfectly uniform, supply of water; by the adaptation of the various reservoirs, aqueducts, basins, and self-acting sluicesas will be seen by the description of the parts which they respectively perform.
The embankment of the great reservoir, which is sixty feet high from the bottom of the rivulet, is now very nearly, and in a few months will be entirely, finished.
This reservoir contains two hundred and eighty-four millions, six hundred and seventy-eight thousand, five hundred and fifty (284,678,550) cubic feet of water; and covers two hundred and ninety-four and three-fourths imperial acres of land.
The compensation reservoir contains fourteen millions, four hundred and sixty-five thousand, eight hundred and ninety-eight (14,465,898) cubic feet of water; and covers about forty imperial acres. Its embankment is twenty-three feet high from the bottom of the rivulet.
The auxiliary reservoir, No. 3, contains four millions, six hundred and fifty-two thousand, seven hundred and seventy-five (4,652,775) cubic feet of water; and covers about ten imperial acres.
The other auxiliary reservoirs, Nos. 1, 2, 4, 5, and 6, are now about to be formed, and will contain something more than six millions cubic feet of water.
Thus, the reservoirs already formed, contain three hundred and three millions, seven hundred and ninety-seven thousand, two hundred and twenty-three (303,797,223) cubic feet; and when the other five auxiliary reservoirs are finished, the whole will contain above three hundred and ten millions (310,000,000) cubic feet of water.
Anxious to obtain information as to the actual condition and performance of these remarkable water works, and unable personally to visit Scotland, I have to thank one of the most eminent men that country has presented to the practical sciences, for a note descriptive of the power that is now produced by the water so economized. Mr. Scott Russell replied to my inquiries in the following words:
My dear Sir,
I had hoped to have been able to get a full and very satisfactory account of the Shaw's water drawn up for you by a competent engineer, resident on the spot; but I find that so many delays are occurring to prevent this, that I now write to beg you will not calculate upon it: had my own time permitted I should have done so myself, but now just when I might have hoped for leisure, I am taken from home.
I have, however, procured a copy of a now scarce pamphlet, printed some thirteen or fourteen years ago, before the works were finished, giving some account of them as proposed. I may now add for your information, that every thing predicted has been satisfactorily and fully accomplished; that the Company now divide a fair percentage on their capital, even though at present only one-half of the capabilities of the reservoir are employed. There has in all years been an abundant supply.
I may also add, that the sole supply of water here obtained is from the fall of rain, and that the artificial lake has been created in a place where formerly there were only slender mountain rivulets.
The guaranteed and realized supply of water amounts to 2500 cubic feet per minute during 310 days per annum. The total fall is about 500 feet; the total power thus created is, therefore, as follows, in round numbers:
2500 feet of water.
60 lb weight.
500 feet fall.
50)75000,000(1500. Steam engine mercantile horse power.
Or about 2000. Bolton and Watt's estimated horse power.
Thus then a power has been created and brought six miles and a half to the suburbs of populous towns, equal to the power of thirty steam engines of fifty horse power; being equivalent to the creation of wealth or productive capital to the extent of £75000; and the annual effect of which, when fully employed, will be something like the employment of 7000 people, and the
p.97annual distribution of something like £300,000 per annum in wages in a single town; besides the supply of ample store of water for the use of the town.
Such, my dear Sir, is a hurried sketch of what has been accomplished: the accompanying pamphlet will tell you something about the details. What further may be necessary for your purpose let me know, and I shall try to send it you.J. Scott Russell.
The greater number of Irish rivers are more or less analogous to the Shannon, in having lakes either at their origin or on their course, and hence present facilities for the accumulation of water power of the highest interest to the mechanical engineer. The concentration of the waters of a district in such reservoirs, by appropriate embankments, may be, and in most cases must be connected with another operation of the greatest importance to the agriculture of this country, the drainage of the surface. As an example of how both objects may be at the same time secured, and how well the physical circumstances of the country lend themselves to their accomplishment, I may notice the relations of Lough Ennell, near Mullingar, to the River Brosna, by which its waters are carried to the Shannon. The facts are taken from Mr. Mulvany's report.
The catchment basin of the Brosna discharges almost altogether into the lake, the waters flowing directly to the river course being comparatively trifling. The difference of winter and summer level is but two feet, yet by this a great extent of land is flooded. Mr. Mulvany proposes to deepen the channel of the lake and river by these two feet, by this means relieving the flat lands, and rendering the winter accumulation of water available for the supply of the mills upon the river during the dry summer seasons.
The area of Lough Ennell is 3603 acres, and at two feet in depth it should discharge 314,000,000 of cubic feet. As in the case of the Dodder, this supply would probably be available twice in the year, for the midsummer floods, though not so great as those of winter, will be in all cases sufficient to replenish such reservoirs. Hence, as the difference of level of the Brosna
p.98issuing from Lough Ennell, and where it joins the Shannon, is 154 feet, a force continuous through half the year of 692 horse power, or four and one-half horse power per foot of fall, should be made available.
The River Dodder, although trifling in magnitude, is yet of much interest to us, from the amount of industry which it sustains in the immediate neighbourhood of Dublin. There are situated on its banks at present twenty-eight mills occupied with various manufactures, as paper, flour, woollens, cloth, &c. This stream, passing by a highly inclined channel from the flanks of the Dublin mountains to the sea, is liable to very great fluctuation in the amount of its discharge. It frequently has done great damage to the lands and edifices along its banks, by sudden floods, and in summer its waters fall so low, that the mills may be considered as being kept idle half time for a period of three months in the year.
At present the occupied fall upon the Dodder is 370 feet. The total horse power, which is now precariously available, is estimated at 926, which is two and a half horse power per foot of fall. The question of rendering the supply of water more uniform, and of economizing a larger proportion of its force has been recently taken up by the Board of Works, at the request of the mill-owners upon the river, and an accurate survey and report have been drawn up by Mr. Mallet, whose union of scientific and practical skill is so distinguished.
Mr. Mallet proposes to form, by means of an embankment about 2000 feet long, and 100 feet high at its centre, across the head of Glenismaul, a reservoir with an area of 162 statute acres, and capable of containing 228,000,000 of cubic feet of water. The catchment basin of this reservoir would have an area of 6070 acres, chiefly mountain bog, and from the quantity of rain which falls in that hilly district, Mr. Mallet calculates, that the reservoir should be filled at least twice in the year, and hence a total annual quantity of water of 456,000,000 of cubic feet obtained, which Mr. Mallet values as equivalent to 1387 horse power in constant operation.
On the construction of this reservoir, it appears by Mr. Mallet's report, that the total force of the river should become
p.99practically equivalent to 2038 horse power. This is five and a half horse power per foot of fall, more than double that now irregularly in operation. The probable cost of these improvements may be taken at 86s. per annum per foot of fall, or 23s. per additional horse power. That is, the expense is just one-tenth that of the corresponding steam power, or one-seventh that of the mere coals for a steam engine.
As I discussed the question of the cost of power so fully when speaking of the production of steam, it will suffice to notice briefly the circumstances of water power as to cost. It is only necessary to contrast it with steam power. It is certainly much cheaper, not merely in Ireland, but in all places where it is available. An eminent manufacturer in Leeds said to me, that water power is cheaper than steam at the mouth of the coal pit. All evidence bears this out. In Mr. Fairbairn's report, and Mr. Bateman's letter, this point is decided, as regards the Upper Bann. Even at present it may be taken at £3 per annum per horse power,steam costing from £20 to £30; it may thus be averaged at one-eighth. But Mr. Bateman considers, that when the reservoir system is worked out, the horse power will be had for 20s. per year, not one-twentieth of the cost of steam
Regarding the Shaw's water works we also have money estimates, which are highly valuable, as they place the relative cost of power by water and steam in contrast, not merely for Ireland, where steam is dear, but for the banks of the Clyde, where coal is at its lowest price. Mr. Thorn thus describes the system followed in Glasgow, which is different from anything here. With us a builder speculates only in houses, in Glasgow he speculates in cotton mills.
I have stated the cost of steam power at £30 for each horse power. Let us see its market price in Glasgow: there it is customary to provide a house for the manufacture, with the steam engine, great-gearing, and steam-pipes,and keep the engine going twelve hours a day, and heat the work,for £50 for each horse power.
The cost of erecting a mill or factory, capable of containing machinery for the cotton manufacture to the extent of thirty
p.100horse power, with the great-gearing and steam-pipes, but exclusive of steam engine and engine-house, may be taken at £4200. Allow the landlord 8 per cent. on this sum, £336, and for heating the house by steam, £84, together £420; which is a fair return for every thing except the steam power. But the landlord draws for the whole a rent of £1500; which leaves for the power a rent of £1080: divide this by 30, the number of horse power, and it gives for each £36 annually.
The average water rent for each horsepower at Greenock is £3; the average rent for two acres of land, to be fued along with each mill site if required, is £16. The work being of fifty horse power, take one-fiftieth of this sum (6s. 5d.) for each horse power. Interest on £2000, the cost of a water wheel, arc, trows, &c, for a work of fifty horse power, £100; one-fiftieth of which is £2, making the whole cost of water power, for one horse power at Greenock, £5 6s. 5d.
Thus each horse power, by water at Greenock, costs upon the whole £5 6s. 5d., being £30 13s. 7d. less than the cost of one horse power by steam at Glasgow. Besides, this calculation includes the rent of two acres of land for each mill at Greenock, whereas at Glasgow no land is taken into the account, except the spot on which the work stands. Were the same quantity of ground given to the mill at Glasgow, at the rate it brings there, it would throw the balance still more in favour of Greenock.
Thus, whether we take Mr. Bateman's value, which is for the bare supply of power; or Mr. Thorn's value, which includes the delivery of the power in a working form, we see that the cost of water power is not more than one-tenth of the cost of steam. Why then is steam so much used? In the first place, water power is available only in certain localities, where other more influential circumstances may forbid the introduction of manufactures; and secondly, the influence of the cost of power is generally so small in mechanical industry, that the question of saving in regard to it is swallowed up in more important questions. Still, wherever water power is to be had, it is always employed in preference to steam, as I shall, in fact, show; but it is first necessary to notice an objection to water power, of a very absurd kind, which, however, requires refutation,
p.101because expressed by a person who influences public opinion extensively in Ireland. He asserted publicly and in print some time ago, that there was an inherent defect in water power that must prevent its being ever extensively used in industry. He said that the water soaking into the wheel at night rendered whichever side was then undermost the heavier, and this preponderating afterwards, gave an unequal and jogging motion which unfitted the wheel for any delicate work. In fact, this learned and eloquent individual had never seen a proper water wheel; had probably never been in a factory; had most certainly never looked at a report of a factory inspector; was too eager in the pursuit of an exalted professional destiny, to consult any merely mechanical person before rushing into public to declaim against the idea of our having any means of becoming industrious in Ireland. Some dream of childhood's rambles along a brook, in which he visited a ruined mill; its wheel dilapidated; its inner machinery groaning at every turn, formed his knowledge of our capabilities for manufacture, and such are the guides to whom we are to look with deference and admiration.
I shall transcribe, in order to preclude further misunderstanding on this point, one passage from the article Steam Engine, in the Encyclopaedia Britannica. The article is written by Scott Russell.
Mr. Lucy had constructed at Birmingham a flour mill driven by steam; and it had been his object to obtain perfection without any limitation of expense. He had got one of Bolton and Watt's best steam engines, and yet he found that his mill neither produced such perfect flour, nor moved so smoothly as mills driven by water. On the contrary, it was found the irregularity of the motion produced a larger quantity of coarse than of fine flour, at a mercantile loss to the owner; and it was likewise found that the irregular propulsion a tergo interfering with the uniform motion, towards which the millstones tended by their own momentum, produced a clanging reciprocation along the whole line of toothed gearing, which was most injurious, and rapidly destructive to the toothed wheels. When we visited the spot in 1838, the ruins of former
p.102wheels, most unequally worn and totally destroyed, were strewed about the yard. The usual plan of increasing the weight of the fly-wheel was resorted to without success; and Mr. Lucy applied to Mr. Buckle to propose a remedy for the evil. This remedy Mr. Buckle found in the very simple contrivance of a pneumatic pump.
So perfect was the action of this mechanism, that the fly-wheel had been wholly removed, and the engine and the whole mill-work were moving in the most smooth and effective manner. It was found that the change enabled them to give all the grinding stones a greater velocity than formerly, so that the quantity ground was greater, in the proportion of 56 to 52, and the quantity of the finest or first flour, from the same wheat, was likewise much increased; so that, both by quantity and quality, the owner of that mill was now able to command the market. The same motion has subsequently been applied to cotton mills with perfect success; the quality and the quantity of yarn produced being much improved.
Now it may be observed that Mr. Russell does not proceed to explain that water power may be employed, but to describe the endeavours of engineers to render the steam engine as regular and as useful for delicate work, as the water wheel is found to be. In fact, cotton spun by water power bears, and has always borne, a higher price than cotton spun by steam power. Moreover, if we analyze the power employed in England in the spinning and weaving factories, we shall have very conclusive evidence on the point. In the estimate of the state of the cotton manufacture in 1833, drawn up by Mr. Baines, and of which the principal items are given in page 59, he considers that of the 44,000 horse power employed, there are
Steam power, 33,000.
Water power, 11,000.
But we have much more complete and more accurate numbers given in the Returns of the Factory Inspectors for 1839, of which the following is a summary.
The total mill power in factories subject to inspection in England was 83,264 horse power.
p.103Of this there were,
In Lancashire, where coals are so cheap, we might suppose that no body would use water, but we find:
Total mill power inspected in Lancashire is 36,446 horse power:
Steam, 32,123 horse power.
Water, 4,323 horse power.
Thus, one-ninth of the total mill power of Lancashire is water power. But in order to estimate how far water power is valued, we must learn, not merely how much is used, but how much is left unused. Now I have endeavoured to calculate on the same principles as I adopted for the surface of Ireland in the beginning of this chapter, the theoretical water power of Lancashire. I have found that it is represented by 72,600 horse power, taken as working continuously. Now the 4323 horse power economized, makes 6 per cent. of the entire; and as there are in Ireland a million and a half of such horse power, it follows that if we economize our water power all over Ireland, in the same degree that water power is actually economized in Lancashire, we should have at work a force of 90,000 horse power, that is to say, greater than the mill power of England as returned by the factory inspectors.
This shews how water power is valued in Lancashire. In fact advantage is taken of every possible situation. The River Irwell, which passes by Bolton and Manchester, and washes the heart of the factory districts, is the hardest worked stream probably in the world. It has, from its first mill at Bacun to Prestolee near Bolton, a fall of 900 feet, of which 800 are actually economized by mills. I do not know another example of such complete application of water power than in that place, where coal is on all sides available. We may, therefore, pass away from this question, of whether water power answers for
p.104mechanical purposes, which I should not have at all noticed, but that the public often receive a bold statement from a public man, without troubling themselves to examine whether it be likely that he understands what he talks about.
Contrast with this the actual economy of water power in Ireland. By the returns of 1839, there were employed in Ireland:
Steam, 1503 horse power.
Water, 2147 horse power.
It has been found that to give to water power its full economy and value, it is necessary to secure its steadiness of supply by the construction of reservoirs, in which such quantity of water may be retained as shall suffice for the average performance of the machine during the entire year. Another mode of compensating for the deficient supply of water in dry seasons remains to be described. This consists in having also a steam engine of such power as to be supplemental to the water wheel, and according as water fails, to work the engine, so that the mechanical force exerted by the steam engine and water machine together, may be constant. This mode is actually adopted in many localities. In the factories of Messrs. Malcolmson at Portlaw in Waterford, two engines of a hundred horse power, and two overshot wheels, of nearly equal force, thus work together. There is no mechanical difficulty in the co-adaptation of these prime movers. Where circumstances prevent the formation of great reservoirs, which, indeed, must perhaps always require the co-operation of several manufacturers, and, therefore, become practicable only in certain localities, the union of steam power with water power, so as to combine the economy of the one with the convenience of the other, presents probably a result beyond which industry need not go.
I have so far described the amount and the application of water power, as it is derived from the residual rain water flowing down the declivities of the country to the sea. This is, in fact, all that is popularly understood by water power; yet it is far from being the only source of mechanical industry which is derived from water. Another of great interest remains to be considered.
From the observations hitherto made it appears, that around the coasts of Ireland the tide rises through a height, which may in average be taken at twelve feet. Our tides are derived, that is to say, they result from the action of those vast masses of water in the great oceans, which being raised above, or depressed below their proper level by the attractive forces of the sun and moon, force, in regaining their position, into, or draw from, the narrow seas and channels, such as ours, quantities of water, which thereby form true currents, as much so as the current of a river, and are equally available to produce mechanical effects. Hence the motion of the tide becomes a source of power, and tide mills form an important variety of water mills. In England they are scarcely used, coals being so cheap, but to us, by proper application, I am convinced they may become an important basis of industry. In order that the force available from the tide may be properly understood, it not being much noticed in mechanical books, I shall proceed to describe the principles of its application more in detail, than otherwise I should deem necessary.
If we conceive a reservoir situated near the shore, and separated from the sea by a narrow canal, and that at low water the reservoir is dry, we will have the conditions necessary for the economy of motive power. Let the canal be provided with a sluice, and waiting until the tide has risen to a certain height, say two feet, let the sluice be opened, and the water let in, in such quantity that it shall rise in the reservoir as rapidly as the tide rises outside. Hence, through the period of the influx of the tide there will be a current through the canal, with a head of two feet. Finally, the reservoir fills to the same height as the sea outside. Then let the sluice be closed, and remain closed, until the tide has fallen two feet. On opening the sluice the water of the reservoir flows out with a head of two feet, and will continue until the tide is out; the reservoir will then empty itself, and be ready for repeating this operation the next tide.
Now let us consider how this is circumstanced as to time. We may take the duration of a tide as twelve hours twenty minutes, and as the tide in average rises and falls twelve feet
p.106in that time, the mean rate of motion of the tide, in height, is found to be one foot in thirty-one minutes. We may take half an hour to a foot without sensible error. Now the tide being out, the sluice must be closed for an hour, in order to allow the water outside to get the head of two feet, with which it has to work. On opening the sluice, it will then flow into the pond, and so continue for five hours, when the tide will be fully in. The reservoir being then allowed to fill completely, for which there is ten minutes available, with additional sluices, the canal is to be closed for an hour, until the sea outside shall have fallen two feet. On opening the sluice the water will issue for five hours, with a two foot head, and then, by the extra sluices, the remaining water of the reservoir may be got rid of in ten minutes, so that it shall be ready to begin again.
The current is thus, with two feet head, for five hours on the rise, and five hours on the fall of each tide; that is for twenty hours out of the twenty-four. Let us now calculate the theoretical power of this current. As a standard reservoir we shall take an area of an acre. When the tide is fully in, the water in the reservoir shall be as deep as the tide rises, that is twelve feet. Of this, however, the two feet that entered last is supposed not to have been mechanically employed. The water of the reservoir which may be used as power is, therefore, ten feet deep. The acre contains consequently 435,600 cubic feet of water. This quantity passes in twice, and passes out twice in every twenty-four hours; that is, in the twenty-four hours there are available, 48,400 tons of water falling through two feet. Now as 884 tons falling twenty-four feet in twenty-four hours is a horse power, it follows, that the theoretical power of the tide, used with two feet fall, is four one-half horse power for each acre of reservoir, in which the depth of water is equal to the height of rise of the tide. Hence, ten acres of reservoir should give a theoretic force of forty-five horse power for twenty hours out of the twenty-four.
Now if this were as in an ordinary stream, nothing could be more simple than the erection of an undershot wheel, which, economizing one-third of the theoretic power, should deliver one and a half working horse power for each acre of reservoir.
p.107But it is easy to observe two circumstances which render the construction of tide-mills more complicated, and their application more difficult. In fact, the current of water changes its direction every six hours, as the tide runs in and out. This, however, is easily met by mechanical contrivances of various and simple kinds, by which the direction of action of the current is altered, when its own direction changes, so that the motion transmitted to the machinery remains the same. This, therefore, is not a real difficulty, although it introduces some additional mechanism. But it is more important to consider, that as the level of the tidal water is continually changing, at the rate, indeed, of two feet in height per hour, the machinery capable of acting at the lower levels of the tide, should be totally submerged at the upper; particularly if in place of the average rise and fall, which we have taken at twelve feet, we consider the rise and fall at springs, which we may estimate at eighteen feet upon our coasts. From this comes the greatest difficulty in managing tide-mills. It is, however, surmounted in either of two ways, which I shall but briefly notice.
In the first the force of the water is applied to bear up the wheel itself, so that it shall constantly float, rising and falling with the tide. This object has been effected, by letting the pressure of the water act on a water-tight frame, within which the whole mechanism of the wheel is contained. It has been also done by making the extremities of the axle of the wheel rest on the pistons of an hydrostatic press, into which water was injected by the wheel itself. All these means are quite practicable; they are not expensive, but they are troublesome, and the necessity for them has probably been the principal cause of the neglect into which the tide-mill has fallen. The second means of compensating for the change of level in the water consists in employing peculiar forms of wheel, of which many kinds have been proposed, which work even submerged, or, at least, admit of being partly submerged without their power being all destroyed. Such wheels have been described by Belidor, Barlow, and other writers, but I shall not delay upon them. They have the merit of turning round when almost
p.108drowned, but they have the fault of not being able to do any important proportion of work. The loss of power in such wheels is so great as to negative their practical employment.
It is thus easily seen, that I do not strongly recommend those tide-mills, which are at present known, whether they work nearly submerged at a constant level, or that they change their level by the aid of complex machinery. I should not in fact, direct attention to the tidal waters as an important source of power, but that there has been recently invented a machine, which I conceive renders them truly available. It is the turbine, already noticed under another point of view. The acting force in the turbine is proportional to the difference between the pressure of the water inside and outside of its cylinder. It is no matter how deep it may be under water, provided this difference is kept up. It works with the same effect; delivers out in practice the same percentage of the theoretic power; and hence realizes absolutely the conditions necessary for the perfect utilization of the motive powers of our tides. If, returning to the example of canal and reservoir, which I already employed, there was placed behind the sluice a turbine, and the water let on at the head of two feet, the turbine would deliver out practically two-thirds of the calculated force, at least, and continue to do so all the time that the rise or fall of the waters continued. The mechanical arrangements for the change of direction of rotation, for conducting the water to and from the top and bottom of the machine, are such as will present themselves to the mind of every mechanical engineer, and would be of too purely technical a character for me to notice here.
The turbine is, therefore, peculiarly the machine for economizing tidal power. For each acre of reservoir it may be expected to give at least three horse power, working twenty hours out of the twenty-four. In average for thirty-three acres of reservoir, on which the flood rises in average twelve feet, a working efficiency of 100 horse power may be calculated on.
Now let us consider how many situations on our coasts there are, where flats left bare by the retreating tide, and covered many feet deep with water on its return, utterly useless in their
p.109present state, only require an embankment easily and cheaply constructive, to be converted into reservoirs for setting tide-mills at work. How many places are there, especially on our eastern coast, where reservoirs of vast size appear, indeed, as if presented by nature to tempt man to enterprize, leaving but little for him to do. Ballyteigue Bay on the Wexford coast is an example of such an inlet; narrow at the mouth; capacious inside; formed as if laid out by a skilful engineer, but its tides, being complex from local causes, counteract the advantage of its form. The inlets along the shores between Dublin and Drogheda present also many similar, though not so curiously affected in adaptation. The areas included between the Kingstown Railway and the shore, may serve to exemplify the facility of embanking such reservoirs, and the tidal currents by which they are filled and emptied. I shall not attempt to calculate the mechanical power that might be created in those situations; I shall leave it as a useful exercise to those, of whom I hope there are many, who may be led by what I have now stated, to think and examine for themselves, and apply the bases of calculation which have been given in this and the preceding chapters to those instances, and to such others as their own observation may bring before them.