12 Trans. Acad. Sci. of St. Louis. 



of this gap, the region covered by the distorted drainage 

 lines become a dark space as is shown in former papers. 

 See also Fig. B of Plate I, of the the present paper. 



Discharge Through Solid Conductors. 



In the former paper, No. IV of Vol. XIX, of these 

 Transactions, reference was made to a form of electrical 

 pumping service, in which a charged sphere is assumed 

 to collapse in such a way as to maintain a constant po- 

 tential, while current is flowing from it through a resist- 

 ance R to a sphere of zero potential and infinite capacity. 

 A better example may be cited as follows: 



Suppose a copper wire of radius r and length L to be 

 surrounded by a co-axial surface of radius /. The two 

 surfaces form a condenser of capacity 



L 



C 



2 log^p 



where p = - . 



T 



Ground the outer shell, thus keeping its potential zero. 

 Charge the wire core to a potential V. Connect one end 

 of this core to a ground of infinite capacity through a 

 resistance 



ks 



Move the condenser towards the resistance R with a 

 velocity v, and assume that the condenser-wire collapses 

 longitudinally at the point where it makes contact with 

 the resistance E. The velocity v is to be so adjusted that 

 the potential V remains constant. The current delivered 

 to the wire of resistance R is then 



■^dQ dC ^ V dL 

 dt dt ^ 2 log^p dt 



The velocity with which the wire must move is 



V = ^^ = 2 logep y=2 logePj^ 



