337 
AC and B,, A'O’; BD, BD’, each equal in length to £AC, are 
rods moveable about the fixed pins DD’. 
Sees Serer e—: pe 
1eSemems Sam fics 5 nan I OES CD 
TV, VW, WY are equal rods connected by pins at V and 
W. VW is attached to AA’ by a pin through its middle point 
R. Tand Y are pins fixed in the framework. R therefore by 
a Watt’s motion describes an approximate straight line per- 
pendicular to 4A’. Now AA’ is parallel to BB’, and therefore 
to DD’, which is a fixed straight line. Hence AA’ moves 
parallel to itself. — 
:. A, R, A’ describe parts of straight limes perpendicular 
to AA’. 
Hence by what precedes C'C’ moves in a fixed straight line. 
