HOW WORK IS DONE 



sprocket wheel that constitutes a lever of the second 

 class with gain of power; where (2) power is further 

 augmented through transmission from the relatively 

 large sprocket wheel to the small sprocket of the axle; 

 and where (3) there is great loss of power and corre- 

 sponding gain of speed in transmitting the force from 

 the small sprocket wheel at the axle to the rubber rim 

 of the bicycle proper, this last transmission representing 

 a lever of the third class. The net gain of speed is 

 tangibly represented by the difference in distance 

 traversed by the man's feet in revolving the pedals, 

 and the actual distance covered by the bicycle. 



INCLINED PLANES AND DERRICKS 



A less obvious application of the principle of recip- 

 rocal equivalence of distance and weight is furnished 

 by the inclined plane, a familiar mechanism with the 

 aid of which a great gain of power is possible. The in- 

 clined plane, like the lever, has been known from re- 

 motest antiquity. Its utility was probably discovered 

 by almost the earliest builders. Diodorus Siculus 

 tells us that the great pyramids of Egypt were con- 

 structed with the aid of inclined planes, based on a 

 foundation of earth piled about the pyramids. Dio- 

 dorus, living at a period removed by some thousands of 

 years from the day of the building of the pyramids, may 

 or may not have voiced and recorded an authentic 

 tradition, but we may well believe that the principle 

 of the inclined plane was largely drawn upon by the 

 mechanics of old Egypt, as by later peoples. 



[37] 



