400 H. V. Gill — Electric Discharge in Geissler Tubes. 



Since the most usual form of the spark in air is oscillatory, 

 we may therefore conclude that the discharge in a Geissler tube 

 is oscillatory likewise. These oscillations may vary in fre- 

 quency from hundreds of millions per second, as in the experi- 

 ments of Hertz, to some hundreds per second as in those of Dr. 

 Lodge. That the oscillatory discharge is the more usual form of 

 a spark appears from the most recent researches. For example, 

 Prof. Trowbridge writes :* " The oscillatory discharge may be 

 said to be the common occurrence in nature in the case of elec- 

 trical discharges, and the one-direction discharge the uncom- 

 mon. ... In general nature avoids an unidirectional dis- 

 charge." 



The stratified discharge may be prod need not only by an 

 induction coil and by an electric machine, but also by a bat- 

 tery of elements in series. . . . 



That the discharge of such a battery is in no way different 

 from the spark discharge produced by other means, is the con- 

 clusion arrived at by physicists. 



De la Rue and Miillerf made use of a battery containing, 

 when completed, some 14,000 chloride of silver cells ; with 

 this battery they performed a long series of experiments 

 which are described at length in their various memoirs pre- 

 sented to the Royal Society. The discharge was found to consist 

 of a number of distinct sparks, when examined in a rotating 

 mirror, making 17 revolutions per second: they add,;}: " When 

 a considerable resistance was added to the circuit, for example 

 4 megohms, the character of the spark was completely modified. 

 "We obtain, at a distance (between a point and a plate) a little 

 less than in the ordinary case, a series more or less rapid of 

 sparks analogous to those of a small Leyden jar, and which 

 pierce the paper by small holes." 



In connection with this statement it will be found useful to 

 consult the paper of Prof. Trowbridge just cited, and in which he 

 says: "Since the discharge from an accumulator of a large 

 number of cells is, in general, oscillatory, I am led to the belief 

 that the discharge from any primary battery is also oscillatory, 

 for in all cases we have to deal with capacity and self-induction." 



We insist on these facts, as they form the basis of the expla- 

 nation we are about to propose. For the same reason it is neces- 

 sary to recall some of the mechanical effects produced in the 

 air by electric sparks. The most familiar of these effects is the 



sents the discharge at high exhaustions — to suppose that they always exist in 

 the spark discharge, but that at high pressures they are so close together that 

 the bright and dark parts cease to be separable by the eye." (" Recent Researches," 

 J. J. Thomson, p. 199.) Our investigation will show that at least the conditions 

 which give rise to the strata are always present in an electric discharge. 



*This Journal, Sept. 189?. fPhil. Trans., 1878, 1880, 1883. 



\ Phil. Trans., vol. clxix, p. 55. 



