ELECTRIC ABSORPTION OF CRYSTALS 



209 



First, the ball h rose and discharged the condenser. 



Second, the guard-ring d ascended. 



Third, the rod q, which had been previously in contact with p, thus 

 bringing the quadrant-electrometer to zero, now moved down and rested 

 on the upper condenser-plate a. Thus any return charge quickly showed 

 itself on the electrometer. The amount of deflection of the instru- 

 ment depends upon the character of the dielectric, its thickness, the 

 charge of the battery, the time of contact with the battery, and upon 

 the length of time of discharging. 



Ill 



In comparing the glass with the crystal plates, the electrometer was 

 rendered as little sensitive as the ordinary arrangement of the instru- 

 ment without the inductor-plate would allow. The electric absorption 

 of the glass plates for a charge in the battery of two or three sparks 

 from the Harris unit-jar then sufficed, after 20 or 30 seconds contact 

 with the battery and 5 seconds discharging time, to give a deflection of 

 about 200 scale-divisions, which were millimetres. The quartz and 

 calcite plates were then alternately substituted for the glass, the same 

 charge and the same intervals of contact being used, and the resulting 

 deflections noted two plates of each substance of the same thickness 

 being used. 



The results of the measurements are given in the following Tables, 

 the effect of the glass being called 100. 



TABLE I. 



April 12, 1880. 



Charge of battery, 2 sparks. 



Contact, 30 seconds. 



Glass (1st plate) 100-0 



Quartz (1st plate) 17-1 



" (2nd plate). 20-0 



Calcite (1st plate) 0.0 



" (2nd plate) 0-0 



(b) 



April 13, 1880. 



Charge of battery, 3 sparks. 



Contact, 20 seconds. 



Glass (1st plate) 100-0 



Quartz (1st plate) 19-3 



Calcite (1st plate) 0-0 



14 



April 14, 1880. 

 Charge, 3 sparks. 

 Contact, 10 seconds. 

 Plates carefully dried by being in desic- 

 cator over night. 



Glass (1st plate) 100-0 



Quartz (1st plate) 10-7 



Calcite (1st plate) 0-0 



(d) 



April 22, 1880. 



Charge, 2 sparks. 



Contact, 30 seconds. 



Plate in desiccator since April 14. 



Glass (2nd plate) 100-0 



" (1st plate) 96-3 



Quartz (1st plate) 13-4 



" (2nd plate) 12-1 



Calcite (1st plate) 0-0 



" (2nd plate) 0-0 



