THE BEGINNINGS OF KNOWLEDGE 



FIG. 1. 



ment of an earlier form, shown in Fig. 2, where a pointed 



stick or drill is twisted by the operator's hands. 

 Let us examine this 



primitive machine more 



closely. The operator, 



forcing the bow back and 



forth, causes its various 



points to move along 



parallel paths. There is 



no turning of the bow, 



so its motion is " trans- 

 lation." The machine 



then converts a motion 



of translation into one of 



rotation. The cord of 



the bow merely replaces 



the hands of the operator. In turning the drill of 



Fig. 2 through one complete revolution each hand 



comes in contact with every 

 point of its circumf erence and 

 moves a distance equal to 

 the circumf erence. When the 

 drill is operated by the bow, 

 the latter must move through 

 an equal distance. The op- 

 erator may use only one hand 

 with the bow, but, obviously, 

 he must push or pull twice as 

 hard since his other hand is 

 not assisting. The advantage 



of the machine is not that it requires less work, but 



that it is more convenient, requiring only the simple 



FIG. 2. 



