On Stationary Electrical Waves in Wires. 383 



that a minute spark precedes the formation of the voltaic arc 

 in air. The medium is first broken down and then the arc 

 follows the drawn apart carbons. I believe that this process 

 occurs also in a vacuum, and that absolute contact is not 

 necessary to start the arc. My experiments lead me to con- 

 clude that under very high electrical stress the aether breaks 

 down and becomes a good conductor. 



Jefferson Physical Laboratory, 



Harvard University, 



Cambridge, Mass., U.S. 



LI I. On the Effect of Capacity on Stationary Electrical 

 Waves in Wires. By W. B. Morton, M.A** 



WHILE working recently at stationary electrical waves in 

 wires produced in Blondlot's manner, I was led to make 

 some measurements on the effect produced when a capacity 

 is inserted at a point of the secondary circuit. The positions 

 of the successive nodes were explored in the usual way by a 

 bridge, the indicator being a vacuum tube which was placed 

 across the wires and which showed a maximum of brightness 

 when the bridge was at a node. When two opposite points 

 of the parallel secondary wires were joined to the plates of a 

 small air condenser, the effect was to bring closer together the 

 nodes on the two sides of the condenser, the amount of this 

 shortening of the apparent half wave-length depending on the 

 position of the inserted capacity. The effect was nil when 

 the condenser was at a node, and maximum when it was mid- 

 way between two nodes. This influence of the increased 

 capacity of the wires is of course of the same nature as the 

 shortening of the wave-length when the wires pass from air 

 into a dielectric liquid. Drude and others have made use of 

 this way of measuring directly the index of refraction of 

 different liquids for the electric waves ; but the influence 

 of an isolated capacity does not seem to have been much 

 studied. Salvioni has published j some measurements on the 

 effect of capacity inserted at a point between the end con- 

 denser and a bridge. When the second condenser was put 

 in it was necessary, in order to restore resonance, to alter the 

 distance of the plates of the end condenser. Von Geitlei't 

 got rid of the reflected waves by using a terminal resistance 



* Communicated by the Physical Society : read April 9, 1897. 

 t Rend. Ace. Line. 1892, pp. 250-253 ; Wied. Beibl. xvii. p. 485. 

 j Wied. Ann. xlix. pp. 184-195 (1893) ; cf. Barton and Bryan, Proc. 

 Phys. Soc. xv. p. 23. 



2G2 



