ble step, or pivot, at o: i i, two vertical rods, which, with a third not seen in the sketch, are attached to the annular sluice gate at equal distances apart, and which being all acted upon equally by an arrangement of screws and spur gear, raise or depress the annular gate with perfect regularity; k k, a leather collar, extending entirely around the upper circumference of the annular sluice gate, which collar being pressed outwards by the water, against the concave surface of the concentric fixed cylinder n n, effectually secures this joint in a manner that prevents leakage; 11, the forebay, the water of which has free communication with the sluices of the turbine, by the whole circular space from k to k; and finally, m is the tail race through which the water escapes, after having actuated the turbine.*

To illustrate still more clearly the construction and mode of operation of the turbines, we subjoin a brief extract from a paper on this subject, by George Rennie, Esq., F. R. S.. &c., published in this journal for 1840, and also reprint the wood cuts accompanying that paper. Fig. III. VERTICAL SECTION.

• We will here observe that the curves of the buckets of the turbine, and of the guides upon the fixed disk, must be traced in a particular manner, which it requires some study to master; and that without a close attention to this point, these wheels may fail to realize a proper degree of useful effect, as was the case with several in France, which were not constructed with sufficient care.

Description of the Engravings.

L, beam with which the lever of the brake is connected by a spring balance marked D. W, water level. F, friction wheel. D, dynamo

meter.

a, Main axle of the turbine.

bb, Shaft pipe enclosing it

C C, The lower part, or shell, of the turbine wheel.

d d, The curved buckets, or vanes, against which the water presses in escaping between them from the wheel.

e e, The curved guides upon the fixed disk.

ff, Rods and screws for manœuvring the annular sluice gate. gg, The annular sluice gate.

"Operation. To set the machine in motion, the sluice g g is drawn up by means of the screws and bolts ff. Then the water which is continually resting on the fixed disk P P, with the pressure of the whole fall, immediately issues out between the curved guides, and impinging upon the curved buckets of the turbine, causes it and the main shaft, with all its machinery, to revolve rapidly."

Such is the description of Mr. Rennie, which is reprinted at the risk of repetition, with the particular purpose of drawing attention to the

Brake, or Friction Dynamometer, of M. De Prony, by means of which the useful effect of the turbine has been usually measured.

The brake consists simply of two stout pieces of wood, embracing a smooth wheel firmly fixed upon the shaft of the turbine, and cut out concave to fit, or nearly fit, this wheel; these collar beams are connected together, by two screws with heavy nuts and washers, by means of which they may be made to embrace the fixed wheel, with any necessary degree of force, or even to stop its motion.

To one of these beams, a long lever is attached, and connected at its outer end, either by a spring balance or a scale and weight, with some fixed point of the building.

This is the whole machine (see the sketches) which, as a dynamometer, is remarkably accurate, as well as perfectly simple; all that is necessary is, that the friction should be made regular, and the wooden collar beams prevented from burning; both these objects are effectually attained, by the simple precaution of causing a small stream of water to fall constantly upon the rubbing surfaces of contact.

Then the screws being set up with any moderate force, weights are added if a scale is used, or the spring dynamometer is made to act, so as to keep the lever fixed in a position perpendicular to the pull of the balance.

If, when the shaft is revolving with speed, the lever remains regulated by the balance weights applied, in the position above mentioned without much vibration, the weight placed in the scale, (or indicated by the spring balance,) multiplied by the velocity the end of the lever would take if free to revolve, will give a correct measure of the net useful effect of the machine.

It was with this simple and correct instrument, devised for such purposes by M. de Prony, that all, or nearly all, of the experiments made by M. Morin and others, upon the economical value of the turbine have been performed.

Comparison between Reaction and Turbine Wheels.

The wheel of the turbine alone, is not very dissimilar in general appearance to the reaction wheel, though totally different in its mode

of action.

The difference lies in the addition of a fixed disk surmounted by curved guides, and in an entirely different curvature given to the buckets; these variations change the whole character of the machine.

The reaction wheel derives its motion solely from the reaction of the spouting water against very oblique vanes, so curved as to facilitate this spouting to the utmost extent; whilst the water is left free to take its own course, in entering the wheel.

In the turbine, on the contrary, the effect is to restrain, as much as possible, the spouting of the water at a high velocity, and force it to act against the vanes, or buckets, almost perpendicularly by its pressure, and not obliquely by its impulse: hence it is that the curved guides are established to conduct the effluent water, and constrain it to act tangentially against the vanes, which are curved around so much as to prevent the water from leaving them until its pressure is exhausted, or until, thrown outwards by centrifugal force, it drops from the wheel inert and almost destitute of motion.

In the reaction wheel, the greater the velocity of the spouting water the greater is the impulsive reaction, and consequently the greater is the effect produced-but in the turbine, the less the velocity of the effluent water, and the less its impulse, the greater is the effect, because its full pressure is then made to act with more advantage.

In fact the turbine is so planned as to satisfy, practically, the theoretical condition which the European philosophers have established as necessary to the production of a maximum effect in water wheels, viz: that the water must enter the wheel without shock, and leave it without velocity-or in other words, that it must be a wheel of pressure and not of impulse-which condition, fulfilled by the turbine, is not satisfied, but reversed by the reaction wheel; and hence it is that the latter ranks amongst wheels of impulse, and has an effective coefficient of only about 0.400, whilst the former takes its place amongst the wheels of pressure, and has a co-efficient approximating to 0.800, or double that of the other.

In fine, if we may be allowed to make such a comparison, turbines are horizontal overshot wheels, and reaction wheels are horizontal undershots; both being similar in action and effect to these, except that in consequence of the water acting in both, upon the whole circumference at once, under full pressure, they admit of being made much smaller in diameter than overshot or undershot wheels; on both of which the water of the fall acts efficiently only by a part (sometimes a very small part) of the periphery.

Experiments demonstrating the economical value of Turbine

Water Wheels.

The first turbine established by M. Fourneyron, after he had completed the plan of his invention, was applied to a saw mill at Pont sur l'Ognon, in France, and a series of experiments were there made by him, to satisfy himself concerning its value as a motor; but although these were perfectly satisfactory, he waited with commendable caution, until he had constructed and put in action several other turbines, (all

of which performed well,) before he publicly communicated the results.

Having obtained a patent for his invention in France, he wrote a very able essay which is published in the "Bulletin de la Société D'Encouragement pour l'Industrie Nationale," for 1834, and gives a full description of the invention and of several turbines which he had then constructed; one of them upon a fall of four and a quarter feet, being of fifty horses power. The society above referred to, awarded to M. Fourneyron a prize of 6000 francs for the successful introduction of his wheels into use.

The great advantages possessed by the turbines over other known hydraulic motors, as displayed in their work at various mill seats, soon attracted considerable attention upon the continent of Europe; and in 1837, Capt. Arthur Morin, of the French Artillery, a distinguished experimental philosopher, took up the subject with the view of fixing decisively, the economical value of this motor; and he made a careful, impartial, and prolonged series of experiments upon turbines of large size, which were then driving extensive mills at Müllbach and Mousray, in France.

The record of these trials, with remarks by M. Morin, was published at Metz and Paris in 1838, under the title of " Experiences sur les Roues Hydrauliques a axe vertical appelées Turbines," from this work we have derived most of the facts herein embodied, and it will be found well worth an attentive perusal, by persons interested in these subjects.

About the same time also, M. Dieu, a major of Artillery, made experiments upon the useful effect of a turbine, established in the mill of Lepine, which trials were quoted and reduced by M. Morin, in the work above referred to.

Experiments upon the available power of a turbine, were also tried upon one which was established at St. Blaise, in the Black forest, and actuated by a stream of water having the enormous fall of 354 feet!

Finally, connected with a proposition made by M. Arago, to create a small fall in the Seine at Paris, and employ turbines upon it to supply that city with water, in lieu of other contrivances now existing for that purpose; a commission was appointed by the Prefect of the Seine to conduct a series of experiments upon the turbine of Inval, and they particularly examined the effect of backwater upon turbines, arriving, as the others had done before, at the conclusion that the coefficient of useful effect was not sensibly diminished, even when the turbine was deeply immersed in backwater.

As the writer believes that no experience has yet been had in America, with turbines at large, he is unable to quote any experi