RECENT PROGRESS IN PHYSICS. 419 



Different metallic bodies can be placed npon the pins a and h; knobs 

 K, 6|, discs S, 8| lines in diameter, points P, Arc. 



In the first of the experiments now under consideration knobs were 

 used. 



The experiments were made in the following manner : One of the 

 arms was brought into good conducting contact with the inner, the 

 other Avitli the outer coating. The jar or battery was charged as 

 before with the Lane]?ir. Observation was made of the number of 

 sparks which passed in the measuring jar before a discharge of the 

 battery took place at a given distance d between the knobs of the 

 spark micrometer. The unit for d was 1^ lines. 



The results of the experiments are comprised in the following table, 

 s and q having the usual signification : 



Comparing any value of q with those under it in the same column, 

 the quotient is nearly the same as that of the corresponding values of 

 d. Take for example the column headed 4, the case in which a bat- 

 tery of 4 jars was used, we see that the quantity 3.5 gives the striking 

 distance 1 ; a double and quadruple striking distance gives double and 

 quadruple quantity, namely : 7 = 2x3.5, and 13.5 = 4x3.5 nearly. 

 Thus the striking distance in the same battery is constantly propor- 

 tional to the quantity q of imparted electricity. 



The other experiments confirm this. The numbers of the gecond 

 column of values of q, divided by those of the first, give as a mean 

 the quotient 1.92, nearly 2, which is the quotient of the correspond- 

 ing striking distance 2 and 1. 



The second and third, second and fourth, second and fifth horizon- 

 tal series of values of q in like manner give the mean quotients, 



1.47 1.95 2.39, 

 or nearly 1.5 = f, 2 = a, 2.5 = \, 



which are the ratios of the corresponding striking distances. 



The quantity 10,3 divided among 3 jars gives the striking distance 

 4 ; the same quantity (very nearly, viz : 10.1) divided among 4 jars 

 gives the striking distance 3. Thus, with equal quantities of elec- 

 tricity, the surface increasing from 3 to 4, the striking distance dimin- 

 ishes in the inverse ratio of 4 to 3 ; the striking distance therefore is 

 directly as the quantity and inversely as the surface, hence 



a 



d = h- 



