us should be present at every trial, and thus always have a disinterested party to record the readings of the dynamometer and gauges, and the time of the experiment, to serve as a check upon the readings recorded by Mr. Emerson's assistant and taken by him. Mr. Webber was assisted most of the time by Mr. Stockwell Bettes, civil engineer, of Springfield, Mass., who read the gauges and otherwise checked the readings taken and recorded by Mr. Emerson.

All of Mr. Emerson's readings, and such of Mr. Webber's as he desired, were recorded in a book kept for the purpose. These records were kept and all the computations therefrom were made by Miss Charla Adams, who for a long time has been familiar with such experiments and computations as an assistant of Mr. Emerson, and who, I am satisfied from a personal examination of her work, has performed the duty in a careful, accurate and thorough

manner.

Experiments upon the following wheels were all witnessed by Mr. Webber, and part of them by myself:

The computed volumes of discharge, and the percentage of efficiency of the foregoing wheels, as shown in your Report, the proof of which has been submitted to me, have been carefully examined with a view to determine the relative value of the wheels named, and their respective performances under the different conditions and amounts of water with which they were tested.

In the testing of turbines, it has been the practice to first determine the velocity at which the wheel will give its greatest effect

when using all the water that will run through it with the gates or entrance apertures open to their full extent, or at "full gate; then to diminish the quantity of water to three-quarters and onehalf, as nearly as practicable, and to estimate the power of the wheel when running at the same velocity. The experiments at Holyoke were conducted practically in this manner. The best velocity was found for "full gate,” and then the amount of water was diminished gradually in successive experiments to the neighborhood of half the quantity, with the wheel running as nearly as might be at the same speed.

This is perhaps the best way to make such tests, everything considered. But it does not in all cases give the exact relative value of the wheels. Some turbines might give a better result at a different velocity when using a less amount of water, and make their average, say, from half to full gate better than by the former method. The difficulty, however, of getting at the exact velocity at which any turbine would give its best results when using different quantities of water, is too great to warrant such determinations in a series of comparative tests such as were made at Holyoke. The same method must be established for all, and the customary one appears to be the fairest, as no other would probably be agreed to by all the turbine builders. In the practical use of turbines for power, it is rarely the case that a wheel is put in of the exact power required. A margin must be left for an excess of power to meet emergencies, and allowance must be made for an increase of machinery, so that a larger wheel is ordinarily purchased than would just suffice to meet present requirements. For this reason, it is not the wheel which gives the highest percentage of efficiency at "full gate" that is really the best wheel. There can be no point fixed at which any wheels should be compared, but it is thought that perhaps "three-quarters gate" is about the average point at which wheels are used, and their comparative efficiency at from one-half to their full power sufficiently represents their real value. It would probably be a better comparative test of wheels to get their best velocity at "three-quarters gate" and run them with the same velocity for greater and less quantities. This would give the real value of the wheel better than the present practice, but it would probably not be generally agreed to. In using the terms "full gate," "half gate," "three-quarters gate," etc., the relative quantity of water is meant. The opening of the wheel gates themselves is not considered. Their construction is often such that

opening or closing them a certain proportion does not affect the quantity of water in the same manner. It not unfrequently happens that a slight closing of the gate increases the quantity of water passing through them, so that the gates themselves are deceptive and are no criterion of the amount of water used. The gate opening is sometimes used to deceive the uninitiated in the circulars of unscrupulous turbine builders, calling "half gate" perhaps twothirds the whole quantity of water, so as to give a higher percentage of efficiency, but the only true standard of comparison is the actual amount of water measured as it leaves the wheel.

The experiments upon the before-named wheels have been carefully plotted with the amounts of water and the percentage of efficiency as co-ordinates, and a mean curve drawn through the points for each wheel. These curves have been all reduced to a uniform horizontal scale for the purpose of comparison, so as to obtain their relative efficiency at all proportions of the whole amount of water from half to full gate. The curves of the eight wheels giving the highest efficiency are shown on the annexed diagram. The horizontal scale shows the parts of the whole quantity of water from half to full gate, and the vertical scale shows the percentage of efficiency at all points corresponding to the amount of water indicated.

The average percentage of efficiency for these eight wheels has been computed for the amount of water from half to three-quarters gate, from half to full gate, and from three-quarters to full gate, as shown in the following table:

TABLE SHOWing Average PERCENTAGE AT PART GATE.

By examining the diagram and the foregoing table, the peculiarities of the several wheels will be readily seen. It will be observed that the Houston turbine, which has the highest percentage of effect at full gate, is really the least efficient at from half to threequarters, and from half to full gate, of all those shown on the diagram, and is only superior to the Nonesuch at from three-quarters to full gate, and that by a very trifling amount; so that the wheel which apparently has the highest percentage is really the least desirable for actual use. The Thompson turbine, which has the lowest percentage of those shown, at full gate, rises to the sixth place at from one-half to full gate, and to the fourth place at from one-half to three-quarters gate. The Tyler turbine, which has the second highest percentage at full gate, falls to the sixth place at from one-half to three-quarters gate. The Hercules turbine, which stands third only at full gate, takes the first rank at from half to full gate, or any of its subdivisions. The New American turbine, which stands only fifth in the percentage at full gate, is second only to the Hercules at from one-half to full gate or either of its subdivisions, and, indeed, differs from the Hercules very slightly in its useful effect through the whole range shown.

Taking the average useful effect of the wheels shown from onehalf to full gate as a measure of their efficiency, their relative value is in the order shown in the table.

Among the turbines tested at about the time of the experiments upon the wheels before named, were two very remarkable ones on account of their very different qualities and performance. These were the Rechard, a statement of which is included in your Report, and the Victor, which was used in the gear experiments, likewise attached to your Report. The first-mentioned has a percentage of useful effect of only 69 at full gate, while the latter has a percentage of 92. At thirteen-sixteenths of full gate, the percentage of efficiency becomes reversed, and below that the Rechard is by far the most effective turbine. From one-half to full gate the efficiency of the Rechard is second only to the Hercules, while for the same range the Victor would come fourth in the list.

Neither Mr. Webber nor myself witnessed the experiments upon these wheels, but they are mentioned to show that a high percentage at full gate is often deceptive and does not always indicate the best wheel for practical use.

In the foregoing Report, with the exception of the last two wheels, only such wheels are considered as were tested in the presence of Mr.