420 RECENT PROGRESS IN PHYSICS. 



or, in other words, the striking distance is proportional to the density of 

 the accumulated electricity. 



If this law be generally true, and the striking distance inversely- 

 proportional to the surface of the battery, but directly proportional to 

 the quantity, for equal striking distances, the quantity must increase 

 in the same ratio as the surface. 



In the above table the numbers of the same horizontal series should 

 be always proportional to the values of s placed over them. Thus 



5.5 8.0 10. 3 , ,,, 1 3 1 3. 5 7,0 10. 1 13. 5 ,4 „ 



-3", 4r6, eTT should be equal 2, also — ^, ^:^ i^ equal 3 &c., 

 which is nearly true for the averages. 



Riess found the law, that the striking distance is proportional to 

 the density of the accumulated E, to hold good for the case in which 

 the spark passed between two parallel metallic discs, or between a 

 ball and a disc. 



He found, that under otherwise like circumstances, the striking dis- 

 tance between two discs is greater than between two balls, and that 

 with parallel discs the spark passed not in the middle, but at or near 

 the edge. For a ball and disc the striking distance is greater than 

 for two balls and less than for two discs. 



§ 32. Stbikixg distance of the battery independent op the con- 

 ducting CIRCUIT. — It was formerly believed that the striking distance 

 of the battery was dependent upon the nature of the conducting cir- 

 cuit, that it was greater with good metallic connexion, less with 

 poorer conductors. Eiess has shown that this is not the case. {Pog. 

 Ann.,LIII,l.) 



The experiments were arranged in the following manner : One of 

 the pins of the spark micrometer was connected with the inner coat- 

 ing of the battery by a thick copper wire ; another thick wire of 

 copper led from the other pin to one of the arms of Henley's dis- 

 charger, the other arm of which was placed in good conducting con- 

 tact with the outer coating of the battery. Between the arms of the 

 discharger the following were interposed in succession : 



1. A copper wire 4 lines in length | a line in diameter. 



2. A platinum wire 102 inches long" 0.052 lines in diameter. 



3. A glass tube 8.3 inches long 4.5 lines diameter, filled with 

 water. 



Thus in turn a very perfect, a metallic, an imperfect, though metallic 

 and finally a very imperfect conductor was inserted. The results of 

 the experiment are given in the following table : 



