262 Mode of Registering Force transmitted through a Driving Belt. 



proportional to the force ; and we have only to contrive some 

 method of registering this difference, in order to have a record 

 of the total force transmitted by the belt. 



There may easily be contrived a variety of arrangements for 

 shevi^ing the difference between the motions of the drum and 

 pulley. Thus a pair of indicators may be fitted, one to each 

 shaft, so as to tell the total number of turns made by each ; 

 from this number, by help of the measured diameter, the dis- 

 tance passed over by each circumference can be found, and 

 thus the element for knowing the force transmitted can be 

 had. 



Or otherwise, and this perhaps is the most convenient ar- 

 rangement, a light pulley, having its circumference one foot, 

 may be brought to bear against the belt on the drum, and 

 another against the belt on the pulley ; if these light pulleys 

 have counting geer attached, a simple reading off and subtrac- 

 tion will give the difference of distance. 



Having now ascertained the difference between the motioiis 

 of the drum and pulley, it remains to ascertain by what this 

 must be multiplied, in order to give the force. It is not my 

 object, at present, to enter into the theory of the matter — al- 

 though this theory presents several points of considei'able in- 

 terest — but to give a practical application of the principle. In 

 order to find out the force due to a single foot of difference, 

 we have to run the pulley unburdened for a considerable time, 

 taking notice of the difference of motion, and then loading the 

 shaft by means of a spring friction^trap with two arms, re- 

 peat the observation over as many strokes of the engine or 

 turns of the drum ; in this way we shall have a new difference, 

 and subtracting the one from the other, we shall have what 

 is due to the force as shewn by the friction- strap. 



When the multiplier for one belt has been ascertained, that 

 for any other belt may be approximately computed, if it be of 

 the same material, by having regard to the relative weights of 

 a foot of each ; so that a pair of accurately constructed coun- 

 ters form a portable apparatus, by means of which the force 

 transmitted by any belt may at once be ascertained, the weight, 

 length, and material of that belt being known. 

 Manchester, Ut Scj^t, 1842. 



