the Electrical Dkcharge iu vacuo. 21 



By careful adjustment I have been able to obtain spai-ks of 

 tlie former class only, and then the experiment may be continued 

 iudetinitcly with no striaj visible; but on the slightest alteration 

 in the distance the strise appear. It is, however^ more frequently 

 the case, that, notwithstanding- all the care used, sparks of both 

 characters will pass in irregular succession ; and then the dis- 

 charges will be without strise in some cases, and with them in 

 others. 



It is necessary to mention the above distinctions, as otherwise 

 any person repeating the experiments miglit be deceived, and 

 not succeeding in obtaining discharges without strife, though 

 the discharges were apparently single, would imagine the results 

 I have described to be illusions arising from an error of vision. 



I repeated the above experiments in one of Mr. Gassiot's 

 vacuum-tubes, which showed the strife beautifully under ordinary 

 circumstances; but when the division iu the circuit was carefully 

 made and carried to its fullest extent, the discharges passed 

 without any strise, the tube being filled at each discharge with 

 a uniform glow. 



From the above experiments I am satisfied that in attenuated 

 media, wherein the stripe are well seen when the ordinary inter- 

 rupted currents are used, discliarges may be made to pass which 

 exhibit no strise, and under such circumstances that there is 

 every reason to believe single discharges only pass. Join to 

 this the fact that the appearances of the strife vary with any va- 

 riation of the contact breaker, that the striaj are more numerous 

 and narrower in proportion as the intermissions of the contact 

 breaker are more rapid, v^diich I have observed to be very nota- 

 bly the case, the evidence seems strong, if not conclusive, that 

 the striae or bands are due to the mechanical interference or reci- 

 procal impulsions of two or more discharges, or rather of the 

 medium affected by them. 



I will take this opportunity of mentioning one experiment 

 which I believe to be new and not devoid of interest. ]\I, Pliicker 

 and ]\Ir. Gassiot have ])ublishcd several interesting experiments 

 on the effects produced by magaets on the strife or on the elec- 

 tric discharge in higlily attenuated media commonly called 

 vacua. 



In repeating some of these experiments with a vacuum-tube 

 kindly given me by Mr. Gassiot, 2 feet 9 inches long between 

 the platinum wires, and 1 inch internal diameter, I found that 

 when the ])ole of a powerful Ixu- magnet was brought close to the 

 positive ])latinum iu a certain direction, the visible discharges 

 only passed occasionally and at intervals through the tube, not- 

 withstanding the apparatus went on working, and the con- 

 tact breaker vibrating as usual. After many cxj)eriments, I found 



