To face page 164. 



FIG. 47. The Bicycle Ergometer. The rear wheel of a bicycle is replaced by a copper disk which 

 can be rotated iu the field of a magnet. The strength of the magnet can be varied by the quan- 

 tity of electricity passing through the field coils. The principle is that of the electric brake. 



Kio. 48. The Electric Counter. An armature which is attracted by two magnets is caused to 

 actuate the ratchet on a revolution counter. The instrument is connected electrically with the 

 bicycle ergometer. 



