OBSERVATIONS OF CHANGE OF POSITION 33 



movement in a straight line), and inversely of rectilinear into 

 circular motion, is also seen in fig. 10. A common requirement 

 in mechanism is that rectilinear movement along a given line 

 shall produce circular motion. This is seen in the rectilinear 

 movement of a piston being used to drive a wheel by means 

 of a crank-rod. The model shown may readily be cut out of 

 cardboard and pinned together. The groove c D corresponds 

 with the cylinder, and the part A B acts as a crank -rod, while 

 the circular portion answers to the driving-wheel. By insert- 



Fig. 9. 



Fig. 10. 



ing the point of a pencil through A and B the two paths may 

 be marked on paper. 



Methods of mere transference of motion may be seen in 

 the leather bands by means of which motion is handed on 

 from one wheel or pulley to another where needed. In this 

 case we have the rotation of the rim of the pulley causing 

 ordinary rectilinear motion in the band, and this, when it is 

 needed, is again converted by contact with another pulley into 

 rotary motion. In a locomotive the reciprocating motion of 



D 



