804 Mr. G. T. Bennett on the Parallel Motion of 



piece A is to have rectilinear motion, say vertically up and 

 down, relatively to a frame or base B (figs. 1, 2, 3). To 



Fiff. 1. 



A perspective outline of fig. 2. 

 Fig. 2. 



A model of one form of the Sarrut parallel motion. 



effect this, four connecting pieces RSTU are used. The 

 pieces All SB are consecutively hinged by three parallel 

 horizontal hinges'*; and, again, the pieces ATUB are con- 

 secutively hinged by three parallel horizontal hinges ; the two 

 directions being different. Connected thus with B the piece 

 A has a movement which is rectilinear and vertical. 



* By the term " hinge," here and throughout, is meant, quite generally, 

 any form of connexion which ensures a permanent axis of pure rotation for 

 the relative movement of two "bodies. " Axis," " turning pair," " cylinder 

 pair," " pivot," " pin-joint," are other terms to be found in use with the 

 same theoretic meaning. 



