Description of the Neiccastle Dynamometer. 209 



The operation of the whole will perhaps be more clearly ex- 

 plained by a numerical example. Suppose the disc-plate to 

 make one revolution while the implement travels over 100 feet, 

 and that the resistance of the implement, when equal to 100 lbs., 

 causes the '^ disc^ioheel" to be drawn from the centre towards 

 the periphery of the disc-plate a distance equal to its own radius, 

 then it will revolve in the same time as the " disc-plate ;" and 

 in that case 100 lbs. x 100 feet = 10,000 units of power 

 (10,000 lbs, raised 1 foot high), will represent the force ex- 

 pended in moving the implement 100 feet.* 



Again, if the resistance of the implement be 200 lbs. the disc- 

 wheel will be drawn from the centre of the disc-plate a distance 

 equal twice the radius of that wheel, and it will make two revo- 

 lutions while the disc-plate makes one revolution, that is to say, 

 while the implement moves through 100 feet. The power 

 expended is now 2 x 100 X 100 = 20,000 units, or 20,000 lbs. 

 raised 1 foot high ; hence each revolution of the " disc-ioheel " 

 represents 10,000 units of power expended or work done, and it 

 will be so, lohether the resistance be constant or variable. The 

 instrument is provided with dials and indices, whereby the 

 number of revolutions made by the '•'■ disc-iuheeV in any given 

 time is shown, and the power expended during that time can be 

 ascertained. 



For example, we will suppose that an experiment occupying 

 ten minutes has been made with a field-implement, and at its 

 close the number of revolutions made by the disc-ivheel is shown 

 by the dial-plates of its counter to be 530*5. 



Then let 530"5 = the revolutions of disc-wheel during the 

 experiment. 

 10,000 =z units of power represented by one revolu- 

 tion of the " disc- wheel." 

 10 = the minutes occupied in the experiment, 

 and 33,000 = units of power, which are equal to 1 horse- 

 power. 



T^u .1. u -11 1. 530-5 X 10,000 T. , 



Ihen the result will be, '-—^ = lb horse-power 



00,000 X I'J 

 nearly, 



* This results from the mathematical truth that the circumferences of circles 

 are proportional to their radii. If, therefore, the disc-wheel move a distance 

 equal to its radius, as from i to e, and remain there in contact with the revolving 

 plate, each point in its circumference will in that position consecutively be brought 

 into contact with a point in the inner dotted circle on the disc-plate as the latter 

 revolves ; and since the circumference of this dotted circle and the disc-wheel are 

 equal, the revolutions of the plate and wheel will occupy the same time. If the 

 disc-wheel moves to /, where i f= 2 i e, the circumference of the outer dotted line 

 is double that of the disc-wheel, which, consequently, revolves twice for one 

 revolution of the disc-plate. — P. H. F. 



VOL. I. — S, S. P 



