434 On a new Form of Horse-power Indicator. 



put forward by Prof. Edlund and Dr. Goldstein, in both of 

 which a vacuum is regarded as a perfect conductor. 



In a future paper I hope to explain other phenomena of the 

 electric discharge by means of this theory, and also to apply 

 it to the case of conduction through metals. 



LXV. A new Form of Horse-power Indicator. 

 By Fkedeeick John Smith, B.A.* 



IN transmission-dynamometers and other instruments used 

 to measure, say, engine-power, it is very convenient (in 

 addition to taking the final result by an integrating apparatus, 

 such as that shown at page 87, Phil. Mag. Feb. 1883, by the 

 author of these lines) to be able to see on a dial at a glance 

 without any calculation the rate at which at any instant energy 

 in foot-pounds is being transmitted. In the communication 

 just cited it was shown how the velocity at any instant could 

 be determined. Now, supposing that the velocity could be 

 kept uniform, then the tension of the belt, as shown by the 

 dynamometer spring, would only have to be read and multi- 

 plied by the velocity of the belt in feet per second; and thus 

 after a trial lasting, it might be, for two minutes the horse- 

 power could be determined. The object of the instrument 

 now to be described is to do away with making different obser- 

 vations and calculations, and to enable the observer to see at 

 a glance the rate at which horse-power is being transmitted at 

 any instant. The instrument in its most simple form is shown 

 at fig. 1, where K P is a square dial divided into little squares 

 (not shown); in each little square the product of the numbers 

 at the top and side appear. ABCD and BFGH are two 

 frames carrying the wires AD and HE. KL is the line of 

 velocities; K M the line of tensions. Now, by means of a cen- 

 trifugal speed-indicator, such as that of Young, and the intro- 

 duction of certain mechanism, the wire H E is caused, by its 

 movement across the dial, to indicate the velocity, in feet per 

 second, at any instant; at the same time A D indicates the 

 tension of the belt transmiting the energy, in pounds; and at 

 the point of intersection of the two wires we find these two 

 quantities multiplied together; and thus at a glance we can 

 see what is going on in the dynamometer. E. g. suppose the 

 wire H E cuts 80, it then indicates the rate of 80 feet per 

 second; if at the same moment A D cuts 40, it shows that the 

 tension of the belt is 40 pounds; if, then, we look at the point 

 of intersection of the two wires, we find 3200, i. e. the rate of 

 3200 foot-pounds per second at the instant when the observa- 

 tion was made. JFig. 2 shows another form of the same 

 * Communicated by the Author. 



