MEASUREMENTS 



295 



FIG. 204. 

 Diagram of Amar's braked bicycle. 



to act as a fly-wheel. A steel band which carries weights at one 

 of its extremities, and is attached at the other to a dynamometer 

 with a dial, passes around a groove in this wheel. For a given 

 weight P, P will be indicated on the dynamometer when station- 

 ary, but at a normal pace, at a known speed (P -f- p) grammes is 

 indicated. The value p depends on the friction. The work 

 done is : 



T = 2nrn X p (see also fig. 137). 



The work done by the muscles of the legs is thus measured, but 

 the pedal could be replaced by a crank handle and the arms made 

 to work by placing the whole frame at a 

 convenient height. The number of re- 

 volutions is taken per minute. For 

 greater exactitude an electric device can 

 be fitted to the fork and the wheel at the 

 point c, which will indicate by notches 

 on smoked paper the revolutions of the 

 wheel. A Depre^ indicator may be in- 

 troduced in the circuit (fig. 205). Other 

 types of brakes are explained by figures 

 206 and 207. Finally, it may be men- 

 tioned that Langlois used a bicycle as a 

 Prony brake which absorbs all the work 

 transmitted to an auxiliary pulley, f 1 ) 

 It has already been shown why this Fie.205. 

 arrangement is unsatisfactory ; it is par- Electrical registration of 

 ticularly so at speeds of 90 to 120 strokes the speed of rotation of a 

 of the pedal per minute ( 219). " bic y de wheel - 



Langlois (Comptes Rendus Soc. Biol. 1910-1). 



