The velocity of this may be 55 to 60 of that of the effluent water -a velocity equal to that due to nearly the whole height of fall; hence, the efficiency becomes "about double that of the ordinary undershot wheel." This wheel has not been much employed in Great Britain, although frequently used in France and Germany. The overshot wheel is most generally employed in Great Britain, for falls beyond 10 feet in height, and some excellent examples occur for work of every description, from rolling iron to spinning silk. Its efficiency averages 66 per cent., but has risen as high as 82 per cent. The economical use of water as a moving power, varying in particular cases, rendered desirable the discovery of a receiver capable of general application, in all circumstances of height of fall, quantity of water, and amount of work to be done; and after intense study, Fourneyron produced the Turbine, the peculiarities of which form the subject of the paper. The imperfect horizontal water-wheels which have been used for centuries in the mountain districts of central Europe, and in the northern Highlands, are mentioned; then are noticed the experiments of MM. Tardy and Piebert, and the allusion by Borda to horizontal wheels; then a general description is given of the numerous experiments made up to the year 1825, when M. Burdin constructed wheels in which the water was received at the circumference of a vertical cylinder, descended in conduits, placed in a helical form round the surface of the cylinder, and made its escape at the bottom; the efficiency of these wheels was stated to be 75 per cent., but no exact experiments were ever instituted. The defects in all the previous machines led to the invention of the Turbine, as it is now designed by M. Fourneyon; its construction may be compared to one of Poncelet's wheels, with curved buckets, laid on its side, the water being made to enter from the interior of the wheel, flowing along the buckets, and escaping at the outer circumference; centrifrugal force here becomes a substitute for the force of gravity. The mechanical construction of the Turbine is then given, and its action is thus described. The water, when admitted to the reservoir, rises to a certain level, exercising a hydrostatic pressure, proportional to the height of the column, and on the sluice being raised, it escapes with a corresponding velocity in the direction of the tangent, to the last element of the guide curves, which is a tangent to the first element of the curved buckets;— the water pressing without shock upon the buckets at every point of the inner periphery, causes the wheel to revolve,—then passes along the buckets, and escapes at every point of the outer periphery; by which arrangement, the size of the machine, even for a large expenditure of water, is kept within narrow limits. The advantages of the Turbines are stated to be 1st. That they are with like advantage applicable to every height of fall, expending quantities of water proportional to the square root of the fall, their angular velocities being likewise proportional to these square roots. 2nd. That their net efficiency is from 70 to 75 per cent. 3rd. That they may work at velocities much above or below that corresponding to the maximum of useful effect, the useful effect varying very little from the maximum nevertheless, and 4th. They work at considerable depths under water, the relation of the useful effect, produced to the total mechanical effect expended, not being thereby notably diminished. These advantages are stated to have been realized in the extensive practice of M. Fourneyron, of M. Brendel, in Saxony, and and of Herr Carliczeck, in Silesia, as well as other engineers. A comparison of the theory and practice of the construction is then instituted, and the following conclusion is drawn :-That if one Turbine has been constructed, which works well under a known fall, expending a volume of water exactly measured, this Turbine would serve as a type for all others. Knowing the fall and the volume of the water to be expended, the Turbine would be made similar to its type. Its linear dimensions would be those of the type, directly as the square roots of the volume of water, and inversely as the fourth roots of the heights of fall. Its angular velocity would be to that of the type, directly as the fourth roots of the cubes of the heights of fall, and inversely as the square roots of the volumes of water. These practical rules were first made manifest by M. Combe, of the Ecole des Mines. A general review is then given of most of the Turbines, erected by M. Fourneyron, at Pont sur l'Ognon, at Fraisans, at Niederbronne, and at Inval, upon which last were tried the experiments which completely established the reputation of the Turbine as an applicable machine. The details of these experiments are given, whence the mean results appear to be, that the height of fall being 6 feet 6 inches With an expenditure of 35 cube feet of water per second, the efficiency was 63 cube feet 79 126 = 0.71 = 0.75 ,, (for which it was constructed) = 0.87 = 0.81 = 0.80 144 These experiments were tried by the application of Prony's Brake Dynamometer, to the vertical shaft of the Turbine itself. M. Arago's proposition for employing the power of one branch of the river Seine upon Turbines, to replace the wheels at the Pont Nôtre Dame, thus giving about 2000 horse power for supplying Paris with water, is then mentioned, as also the results of experiments with very low falls; showing that With a fall of 3 feet 9 inches, the efficiency of the Turbine The Turbines, at Müllbach and Moussay, are mentioned, as are the failures of several of these machines, constructed by other engineers; and the paper concludes with an account of a Turbine at St. Blazeux, in the Black Forest, where the height of the fall is 345 feet, the quantity of water 1 cube foot per second, and the reported efficiency from 80 to 85 per cent. Mr. Taylor said, that Professor Gordon's Paper, on the Turbine, had been brought before the Institution, with the advantages of illustration afforded by the model, made under the superintendence of Mr. Jordan, for the Museum of Economic Geology, a most useful institution; for the present advanced state of which the country is in a great degree indebted to the zeal and scientific knowledge of Mr. De la Bèche, who conducts the geological survey of the kingdom, ordered by the Board of Ordnance. The Institution was indebted to the courtesy of Mr. De la Bèche, for the exhibition of the model, and Mr. Taylor had been anxious that the subject should be brought forward at this time, as the only period at which such a permission could have been granted; for models, once deposited in the Museum, were not alllowed to be removed. But it had been arrested, in its passage, from the hands of the maker, and thus had been procured for the inspection of members of the Institution. Mr. Taylor then proceeded to remark, that, although the improvements in the application of steam had rendered water-power of less value than formerly, yet there were many situations, particularly in the mining and the highland districts, where it was still employed beneficially. And, as an instance of the extent to which water-power might be applied, he mentioned a case in Devonshire, where, in the adjoining mines of Wheal Betsy and Wheal Friendship, near Tavistock, which have, for many years, been under his management, a fall of water of 526 feet in height, is employed in giving motion to seventeen over-shot wheels, eight of them performing the duties of pumping water from a depth of nearly 200 fathoms. The diameter of the largest of these wheels being 51 feet, with a width of breast of 10 feet clear, within the rings; the smallest of the eight being 32 feet diameter, and the others of intermediate sizes. Four other wheels give motion to machines, for drawing up the ores to the surface, their diameters varying from 40 to 26 feet, and the five remaining wheels are employed for mills for crushing and stamping the ores. In addition to all this power, a steamengine, with a cylinder of 80 inches diameter, and 10 feet stroke, is provided as an auxiliary, in periods of drought or frost. He then gave the distribution of this water-power, in the following tabular form: Overshot Water Wheels employed in pumping water at Wheal Friendship Lead and Copper Mines, near Tavistock, in July, 1841. From Data furnished by Mr. Anthony Rouse, Engineer at those Mines. All the wheels operate on their pumps by means of a simple crank, formed on each end of the centre axis or gudgeon, on which the wheel is mounted. Two long rods extend, nearly in a horizontal direction, from the pins of those cranks, to the upright arms of two bell crank or elbow levers, which are situated at the mouth of the pit or shaft, and, from the horizontal arms of those elbow levers, two vertical pump-rods are suspended in the pit. Those rods and the pump-work are the same as commonly used for steam-engines in Cornwall, with plunger pumps, except that there are two pump-rods in each pit, and they move up and down in contrary directions, owing to the two cranks on the ends of the axis of the water-wheel being bended in opposite directions; by that arrangement the weight of the two rods counterbalance one another; one half of the pumps are connected to one rod, and the other half to the other rod, and the water is raised in the pumps by turns. All the wheels have a considerable length of horizontal rods, to extend from their cranks to the elbow of bell-crank levers at the pit's mouth; and in some cases, a very considerable length of such rods, occasioning much friction. I. Old Sump Wheel, 51 feet in diameter, 10 feet broad. The water poured into its buckets was at the rate of 5632 gallons per minute; which, at 10 lbs. per gallon, would be 56,320 lbs. weight, descending 51 feet 2,872,320 lbs. per minute descending 1 foot; that is, the power of the water expended,—or, being divided by 33,000 lbs. (for a horse power, according to Mr. Watt,) gives 87.0 horse power expended. The wheel, when so supplied, made 5 revolutions per minute, and worked 6 pumps, as follows: |