1012 SUMMARY OF CURRENT RESEARCHES RELATING TO 



stago to the stage-plate keep the parts in contact together, and com- 

 pensate for tho loss by wear, which is on one surface in one direction, 

 to wit, downwards, whilo the wear of the screw is on two surfaces in 



^-b Fig. 20C. 



two directions, to wit, upwards and downwards. In the hands of an 

 active worker this wear of a screw makes an unpleasant loss of 

 motion in two directions, and which it is not easy to remove in the 

 case of a screw. The cam gives the minimum of trouble for wear 

 and loss of motion thereupon. 



In fig. 206 the stage is represented as arranged for use, so that it can 

 be elevated or depressed. When not in use the cam lever is turned so 

 as to lie parallel with the stage, and the stage is not put on a stretch. 



