180 BARUS— METHOD OF STANDARDIZING [April 24. 



the brass plates. Since A is equal 315 sq. cm., ^ = .082 cm., 

 d'=:.6y cm., 



C = 305.6 ( I + .0784) = 330 cm. 



This value will suffice for the present purposes, though it needs 

 further correction by comparison with a standard condenser, not 

 now at hand. 



A special key was provided (Fig. i) whereby C could be 

 switched into the electrometer system or out of it and put to earth. 

 Hence in a series of successive discharges 



(C"-i-c)V={C"^C' + c)V', 

 (C" + c)V'= (C" + C' + c)V", 



etc., so that for n discharges, if the residual potential is Vn 



V{C" + cY=Vn{C" + C + cY, 



from which the total capacity C = C" -\- C -{- c is determinable in 

 terms of C The results were: 



Positive charge, C" + C + c= 1,445, 1.443' 1422, 



Negative charge, C" -)- C -f c = 1,482, 1,480, 



Mean C= 1,459, 



the experiments alternating from positive to negative charge, be- 

 cause of the marked drift by the electrometer system when isolated 

 from the cell, as already specified. To measure the small capaci- 

 ties c, of the fog chamber, the same method with ten discharges 

 suffices, if C" is excluded and C retained. Thus the data were 

 successively found, 



+ Charge, c=ii.8 12.4 12.2 12.9, 



— Charge, c:=io.8 10.4 11. i 11.5, 



Mean <:=^ii.3 11.4 11.6 11.2, 



eliminating the drift in the final mean, c= 11.4. 



Since the capacity c in terms of the effective internal radius R2 

 and external radius R-^ the length / of the clindrical condenser may 

 be written 



log^ = 



/ ^ R 2X2.3X<^' 



