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XXIV. A Hiqli Pressure Spark-Gap used in connexion with 

 the Tesla Coil. By F. J. Jer vis-Smith, M.A., F.R.S.* 



IX October 1896 I showed that an #-ray-photo could be 

 produced by means of an exhausted bulb having no 

 terminals, and in January 1897 the relationship between 

 the position of maximum activity at the bulb and the dis- 

 charge from a Tesla inductor was described. The references 

 are p. 594, vol. liv. and p. 294, vol. lv. ' Xature.' Again 

 returning to experiments with exhausted bulbs having no 

 terminals, I wished to improve the Tesla inductor formerly 

 used by me. When a spark-gap is employed in air at normal 

 or less than normal pressure, the sparks often leap from ball 

 to ball, not by the nearest path, but through a rather long 

 one of curved form [the ends of the curved path often 

 terminating in the equatorial regions of the two balls], the 

 discharge from the secondary coil at the same time being 

 somewhat reduced. With this before one it seemed highly 

 probable that far better results would be obtained if the 

 spark-gap were subjected to pressure. 



In order to put this to the test a spark-gap was constructed 

 as shown in fig. 1, where B is a glass vessel closed with a 



T 



/VG. / 



u 



9 

 o 



f/G.1: 



F/c.2 



f/c.3 



metal lid L, provided with a stuffing-box through which a 

 screwed rod can be moved by means of a micrometer head M; 

 the rod carries the upper ball, the lower ball is attached to a 

 rod which passes through a plug in the bottom of the vessel : 

 a tube T and a pressure-gauge G- are attached to the lid, and 

 also to an air force-pump (not shown) ; one end of the pri- 

 mary coil P is attached to the lid and the other end to the 

 condenser C. The two sides of the condenser are connected to 

 the secondary of an induction-coil, by the wires I, I. S is 

 * Communicated by the Author. 



