58 J. Trowbridge — Side Discharge of Electricity . 



of potential which is greater than that between A and B, 

 which are connected by the small resistance of the rarified gas. 

 This phenomenon suggests a photometric method of com- 

 paring the capacity of large condensers and also of obtaining 

 the capacity of the immediately surrounding space. Fig. 2 

 represents a modification of the tube represented in fig. 1. 

 To the arm C and D of the cross are attached the condensers 

 which are to be compared. At the instant of the completion 



of the circuit with the storage battery under the conditions 

 mentioned above, two side discharges take place from C and D 

 either to A or B. By bringing the light of these two simulta- 

 neous discharges into a suitable photometric arrangement, one 

 can compare the capacity of the condensers to the degree of 

 accuracy obtainable by ordinary photometric determinations. 

 Since it is difficult to obtain an estimate of the capacity of 

 large bodies of irregular shape and of large extent, this method 

 may be of use. By a suitable vacuum tube and proper 

 exhaustion the method does not require a large number of 

 cells. 



It was noticeable that when a stratified discharge was estab- 

 lished between A and B fig. 1, there being no spark gap in 

 the circuit except that of the rarified space between A and B, 



