92 Inductive Capacity of Solids under varying Fields. 



11-030 

 11-052 

 11-000 

 10-998 



10-999 = mean of 160 readings. 

 8*030 = zero-reading of scale. 



2-969 = d A . 

 d 2 = 5'010, c^ =-11*964, and hence K'=5*861. 

 Called K'=5*86. 



These results, then, give the specific inductive capacity of 

 plate-glass 6*2 per cent, less in oscillating than in slowly 

 changing fields. 



Though the relative values of K for glass under these two 

 conditions seemed to be undoubtedly correct, it was not ex- 

 pected to find such a low value for slow fields ; and so, to 

 verify the results obtained, the apparatus was taken apart 

 and put together again with the dimensions changed and the 

 experiment repeated for slow fields. The distances chosen 

 were P = 6*401, c? 2 = 3'524, ^ = 11-964 ; and as the result of 

 thirty readings d A — 1*574. Whence K = 6'14, or 1*8 per 

 cent, less than before. 



These results show that there is a decrease in the value of 

 K for paraffin and glass when the alternations of force are 

 rapid, but that the change is much smaller than several 

 observers have stated. M. Blondlot found K for glass in 

 oscillating fields to be 2*84. J. J. Thomson obtained for 

 glass the value 2*7 (see * Recent Researches in Electricity 

 and Magnetism/ by J. J. Thomson, p. 471 and following). 

 Ewing found the value of mirror-glass by a method of oscil- 

 lations (Physical Review, July and August 1894, p. 51) to be 

 5*84. His calculated value for glass w r as 6'24. 



The above method, it is believed, is capable of giving 

 accurate results if the apparatus be well made, and it is hoped 

 that the detailed description given above will enable anyone 

 to readily repeat the experiment. Should this be done, 1 

 would suggest that the apparatus might with advantage be 

 made considerably smaller. 



I desire to say, in conclusion, that I am greatly indebted 

 to Professor Henry A. Rowdand for suggestions, and especially 

 for the opportunity of performing the experiment'*. 



* The entire original idea of this method and all its details are due to 

 Mr. Northrup, and only one or two "very minor points are my own. — 

 Henry A. Rowland. 



