270 OF THE REGULATION AND [SECT. vm. 



To apply this, let A B be a lever, with a 

 friction strap that may be tightened upon 

 the cylindrical surface of the shaft or wheel 

 C, and let it be tightened by the screw at B, 

 (the lever being stopped by the stop D,) till 

 the friction be equal to the power of the 

 engine when all other work is thrown off; 

 then, while the engine is still in motion, add 

 such a weight at E as retains the lever in a 

 horizontal position. 



To calculate the power. Multiply together the length F C of the lever in feet, 

 the weight E in Ibs., the number of revolutions of C per minute, and the number 

 6'2832, the result will be the Ibs. raised 1 foot per minute ; and, divided by 33000, 

 it is the horse power. 1 



Thus if a shaft C make 25 revolutions per minute, and the length F C of the 

 lever be 10 feet, and if it be found that a weight of 240 Ibs. is sufficient to retain 

 the lever in a horizontal position, then 6-2832 x 10 x 240 x 25 = 376992 Ibs. 

 raised 1 foot, or 11^ horse power nearly. 



The trial is so easily made, and the result so accurate a test of the qualities of an 

 engine, that I strongly recommend it to the notice of those who are desirous of 

 having good engines. 



563. THE COUNTER. To estimate the saving of fuel by the application of 

 Watt's engines, an apparatus was attached to the beam to ascertain the number of 

 strokes the engine made in a given time : it is called the counter, and consists of a 

 train of wheel-work resembling that of a clock, so arranged that every stroke made 

 by the engine moves one tooth, and the index shows how many strokes have been 

 made between the times of examination. The counter is enclosed in a box and 

 locked, to prevent it being altered during the absence of the observer. If the box 

 be attached to the axis of the beam, the inclination of the beam causes its pendu- 

 lum to vibrate every time the engine makes a stroke, and thus moves the counter 

 round one tooth for every stroke. The box may also be fixed to the supports of 

 the beam, and then at every stroke a small detent is moved one tooth. The 



1 For, let / be the leverage the weight w acts with, and r the radius of the wheel or shaft C ; the 



/ MJ 



friction /, the velocity t>, and the revolutions of C per minute n. Thenfv = the power, /= , 



and v = 6-2832 r n ; consequently v f = 6-2832 Iwn, the power in Ibs. raised 1 foot, when / is in 

 feet and w in Ibs. 



