234 



PROCEEDINGS OP THE AMERICAN ACADEMY 



the same thickness as in the previous experiments, viz. Nos. 21, 22, 

 and 23, B. W. G., corresponding to a thickness of 0.032 in., 0.027 in., 

 and 0.024 in., respectively. 



It was feared, however, that further difficulty might be met with 

 from yielding of the supports of the cam-rod when heavy diaphragms 

 were used, so that a modification of the apparatus was thought to be 

 desirable. The cam-rod was therefore provided with a brass dia- 

 phragm-holder, so that the diaphragm, being carried by this, was moved 

 bodily forward by the longitudinal motion of the cam-rod. A series 



