810 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



carried by a mechanical microscope stage, so that the specimen could 

 be moved around under the point terminal until a point of contact 

 that gave the capacity effect was located by the capacity measurements. 

 The pressure of the point electrode was then increased so as to avoid 

 accidental disturbance of the connections during the measurements of 

 capacity. 



Data. — Current-readings on charge and discharge were taken with 

 the crystal charged so that the point electrode was positive and then 

 with the point electrode negative. Table IV. contains the record. 



Figure 10. Point negative. Discharge current vs. n, for various applied 

 voltages V. 



By a reference to Table IV. it will be seen that with the crystal 

 charged so that the point was positive this specimen gives the same 

 current on discharge as on charge. With this direction of charging 

 the crystal condenser shows practically/ no leak. Table V., which con- 

 tains the steady current-voltage data for this specimen, shows also 

 that with this direction of application of the e. m. f the crystal lets 

 through only .09 X 10-'' amperes at 1.2 volts. With the e. m. f ap- 

 plied in the opposite direction (point negative) the charge and dis- 



