506 



Mr. E. C. Rimino-ton on Luminous 



But in view of tLe difficulties of the investigation, the 

 paucity of available material, and the approximate nature of 

 the results in this almost unexplored field, no final decision 

 can as yet be arrived at. A tabulation and a graphic repre- 

 sentation of the results, with diagrams of the apparatus and a 

 full discussion of methods and corrections, will be found in 

 the original paper. 



LII. Luminous Discharges in Electrodeless Vacuum-Tubes. 



By~Ei. C. RlMINGTON*. 



SINCE reading a paper in conjunction with Mr. E. W. 

 Smith on November 25th, 1892, before this Society f, on 

 fl Experiments in Electric and Magnetic Fields, Constant and 

 Varying,-" the Author's attention has been drawn to a paper 

 contributed by Mr. Tesla to the 'Electrical Engineer' of 

 New York, July 1st, 1891, in which the luminous ring- 

 shaped discharge obtained when a Leyden jar is discharged 

 through a coil of wire surrounding an exhausted bulb is 

 attributed to the electrostatic action of the surrounding wire, 

 and not to the electric stress set up in the rarefied dielectric 

 in consequence of the rapidly oscillating magnetic induction 

 through the bulb. 



As one experimental proof of this assertion Mr. Tesla 

 gives the following experiment : — " An ordinary lamp-bulb 

 was surrounded by one or two turns of thick copper wire, 

 and a luminous circle excited by discharging the jar through 

 this primary. The lamp-bulb was provided with a tinfoil 

 coating on the side opposite to the primary, and each time 

 the tinfoil coating was connected to the ground, or to a large 

 object, the luminosity of the circle was 

 considerably increased/' 



The author repeated this experi- 

 ment with two Leyden jars arranged 

 as in fig. 1, and found that when the 

 spark-gap was sufficiently large to 

 produce a bright ring when the tin- 

 foil was not connected to earth, doing 

 so produced no noticeable difference 

 in the brilliancy ; but that, if the 

 discharge were faint, it was ren- 

 rendered considerably brighter on 

 making the earth connexion. Better 

 results were, however, obtained on 



* Communicated by the Physical Society : read April 28, 1893. 

 t Ante, p. 98, 



