PHOCEEBIXGS OF TEE POLYTECHNIC ASSOCIATION. 931 



revolutions of the cone is made to measure the power transmitted in 

 a given time. Attached to this cone is the usual decimal gearing, 

 and index for counting revolutions. 



The manner of adjusting this instrument is as follows : Holding 

 the shaft firmly to prevent its revolving, by means of a strap 

 or lever, we load the pulley to the greatest power it will ever be 

 required to transmit ; then so adjust the cone in relation to the slid- 

 ing boss that the rubber disk presses upon the smallest part, which 

 w^e will suppose to be three inches ; next reduce the weight to one- 

 half, and the pulley will spring back a little, thereby moving the 

 rubber disk to act on a larger portion of the cone ; but at this point 

 it should press on a portion of the cone double what it was in. the 

 first instance, or six inches in diameter, and the steel piece should be 

 fitted so that this result will be accomplished. A suificient number 

 of intermediate points should be established in the same manner, so 

 that at all points the ratio between the force upon the pulley and 

 the number of revolutions of the cone shall be the same. The 

 amount of force then is clearly shown by the revolutions of the cone. 

 But the question of time also enters into power. This is obtained 

 by reading the revolutions at certain fixed intervals of time. The 

 velocity of the cone being evidently the product of the weight mul- 

 tiplied by its velocity, its speed is evidently the measure of power. 

 But its speed is measured by its revolutions. The average of its 

 revolutions is evidently, then, the average of the power transmitted 

 by the pulley, or rather by the spring. In obtaining the average of 

 the revolutions, a divisor is required, which divisor must be such as 

 to bring the answer into units of 33,000 foot pounds per minute or 

 horse powers. Let us suppose the pulley to be thirty-six inches in 

 diameter, and that a strain of 1,000 pounds upon the pulley will 

 bring the rubber disk to a point on the cone where the cone will 

 make an equal number of revolutions with the shaft. Each revolu- 

 tion of the cone will then represent 9,421.8 foot pounds. As a horse 

 power in relation to an hour is 1,980,000 foot pounds, the cone will 

 make 210,084 revolutions per hour for each liorse power. We gear 

 down in this ratio to one, so that on reading the index hourly the 

 horse power is read ofl:' directly in units. In cases where the figures 

 of the divisor are of such a nature as to require inconvenient compli- 

 cation of gearing to apply them, the figures beyond the first two cr 

 three may be replaced by cyphers, and the time of reading the index 

 be extended according to the ratio which the subtracted figures bear 

 to the whole divisor. 



