808 PROCEEDINGS OF THE AMERICAN ACADEMY. 



and on discharge 



C',= cf I -1.5^\ 



(23j 



in which E, is the resistance from the impressed e. m. f. into the con- 

 denser, and p is equal to Y/ E and is the resistance to steady e. m. f. 

 of the circuit from the source of e. m. f. through the leads and through 

 the plates and dielectric of the condenser. The resistance p is a func- 

 tion of E and is smaller the greater E is. 



These equations are consistent with the fact that the coefficient C'^ 

 on discharge is greater than the coefficient C'l on charge. This is seen 

 from Table III. to be true both for A positive and for B positive. 

 Now the current-voltage curves of Figures 3 and 4 show that p is 

 smaller for A positive than for B positive. This would make the 

 coefficients for B positive smaller than those for A positive, whereas 

 the converse is the case. In order to explain this discrepancy it is 

 necessary to suppose either 



(1) that the capacity of the crystal condenser is actually greater 

 in direction B positive than in the opposite direction, or 



(2) that the resistance R is also a function of ^ and decreases with 

 increasing E more rapidly than p does. 



The second of these propositions is entirely consistent with previous 

 experiments with carborundum crystals, which showed that if the 

 electrodes were plated to the specimen a large part of the dependence 

 of resistance on current disappeared. 



We cannot, however, be sure that the apparent inequality of capacity 

 in the two opposite directions is entirely an effect of leak current ; for 

 we give next data obtained with another specimen with which the 

 leakage through the crystal is almost entirely absent, and yet the ca- 

 pacity given by the measurements is different in the two opposite 

 directions. 



Experiment II. Specimen with very Small Leakage. 



Mounting in Wood's Metal. — This specimen of carborundum was 

 mounted in a metallic cup in a matrix of Wood's metal. The Wood's 

 metal which served as a solder was placed in the cup and was melted. 

 The specimen was pushed into the molten solder and held with all but 

 its upper face submerged until the solder solidified, forming a close- 

 fitting mold about the specimen. The cup served as one electrode. 

 The other electrode was a pointed brass rod brought down upon the 

 crystal and held by a spring. The cup containing the specimen was 



