Transmission of Electric Disturbances. 131 



The velocity along a wire in air is thus 5*4/4, or 1*35 times 

 the velocity along a wire surrounded by paraffin. 



Wire surrounded 

 by air. 



6*25 metres. 



ire 



surrounded 



by sulphur. 



4 metres. 



4 



n 



4 



>> 



4 



J5 



6-5 



>> 



7 



J5 



7-5 . 



iy 



6*81 metres 



Mean . . 4 metres. 



Thus the velocity along the wire surrounded by air is 1*7 

 times the velocity along the wire surrounded by sulphur. 



These experiments show that the velocities along wire sur- 

 rounded by air, paraffin, and sulphur are approximately 

 proportional to the reciprocals of the square roots of their 

 specific inductive capacities. 



When the tube surrounding the branch BM of the circuit 

 was filled with powdered glass, the sparks were least when the 

 lengths of the wires BL, BM were equal. This was also the 

 case when the tube was filled with flowers of sulphur. I 

 believe the explanation of this to be that the small pieces of 

 glass and sulphur are coated with a conducting film of mois- 

 ture which prevents the waves entering the glass or sulphur, so 

 that the waves in this case are really transmitted through air. 



Velocity of Transmission along Electrolytes. 



To determine the velocity along an electrolyte, an electro- 

 lytic cell filled with a solution of zinc sulphate and having 

 zinc electrodes was placed in one of the arms of the fork. 

 The cross section of the cell was about 1 square inch, and the 

 distance between the electrodes about 2 inches. In this case 

 the sparks were least when the arms were of the same length, 

 though the effect produced by increasing the length of one of 

 the circuits was not so great as when both arms were entirely 

 metallic. The velocity of propagation of a rapidly alternating 

 current along an electrolyte surrounded by air can thus not 

 differ much from the rate along a wire. 



When a vacuum-tube was substituted for the electrolytic 

 cell, the sparking-length did not seem to be affected, however 

 the relative lengths of the arms BL and BM were altered. I 

 believe that this, however, is not because the velocity of the 

 discharge through a vacuum-tube is very much less than the 

 velocity along a wire, but on account of the retardation of the 

 discharge at the electrodes. The velocity across an air-space 

 cannot be very different from that along a wire, otherwise the 

 periods of electrical vibrators would vary with the length of 



K2 



