SPECIFIC INDUCTIVE CAPACITY 123 



large condenser to that of the electrometer + the small condenser. 

 In order to eliminate the distance of the plates apart, a quantity 

 not easily measured, Boltzmann moved one plate and took observa- 

 tions at different distances, so that the distance the one plate was 

 moved alone came into consideration. The principle of the experi- 

 ment may be represented as follows : 



Let C E be the capacity of the electrometer + small condenser 

 c, and let V be the potential of the battery. When the key k is 

 open and t is connected to a, the electrometer will indicate V. 

 Now let k be connected to e, the electrometer being thus dis- 

 charged. Let t be connected to 6, the large condenser C being 

 thus charged to V. Let its capacity be C l when the plates are 

 distance- d l apnrt. Let t be disconnected from a and 6, and let k 

 be connected toy. Thus the charge on C is shared with C E , and 

 we have the potential falling to V r where 



whence C x = C E _ (1) 



Since the two readings of the electrometer give us V 1 /V, we have 

 C'j in terms of C E . 



Repeat these operations when the distance of the plates in C is 

 altered to </, and the capacity to C r and let the potential after 

 sharing be \ ,. Then we have 



Then insert the slab with dielectric constant K and with thick- 

 ness d, the distance of the plates apart being d y Let the capacity 

 now be C t , and the potential after sharing be V a , and 



c, 



(l).(2),(3) g iveC i: C t :C r 



Since the dielectric is equivalent to -== of air, we have 

 111 ,,d 



c~ c~ : cT = l : * : 3 " K 



1111 ,K-1 7 



whence - -: = d 2 d^: d 3 d == "i 



O Cy Oji V/i 



and K = d 



(*,' 



