OF ARTS AND SCIENCES. 



233 



Fig. 2. 



It will be seen from the demonstration that this transformation of 

 axes without change in the form of curve is peculiar to the parabola. 



The calibration being completed, we proceeded to investigate the 

 law of relation between pressure and current, using the Dolbear and 

 chromic acid primary batteries, and the Brush storage battery. 



The pressure at the contact was adjusted by the spring until the 

 addition of 25 mgr. would allow sound to be transmitted through the 



Fig. 3. 



telephone ; the weight was then increased, at first by additions of 250 

 or 500 mgr., and afterward more rapidly.* The deflections, the 



* In some series the increment was only 25 mgr. 



