796 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Experiment I. 



Crystal held in a Clamp. — In this experiment a flat piece of carbo- 

 rundum, about 1 mm. thick, was clamped between two screws A and B 

 of Figure 2. These screws passed through brass supports P and Q in- 

 sulated from each other by a fibre block F. The screws had copper- 

 plated ends, and were screwed down upon the specimen with sufficient 



1.0 1.2 



Figure 3. Current vs. voltage. A 

 positive, n = 24.2. 



Figure 4. Current vs. voltage. B 

 positive, n = 24.2. 



pressure to cause the brass supporting strips (1 cm. wide and 1.5 mm. 

 thick) to spring apart perceptibly. Later experiments showed that the 

 amount of this pressure probably has no influence on the capacity, so 

 long as the increase or decrease of pressure does not change the posi- 

 tion of the contacts with respect to the conducting laminae. 



Choice of Specimen. — The particular specimen used in this experi- 

 ment and the particular setting of the crystal between the supports was 

 obtained only by groping. It had been found accidentally that a speci- 

 men of carborundum used in temperature measurements of conductivity 

 showed a slight capacity effect. Incited by this observation, we selected 

 a large number of pieces of carborundum and put them one after the 

 other in the clamp and tested for capacity. Most of them showed no 

 capacity. Finally the piece used in this experiment was tried with the 



