THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOUENAL OF SCIENCE. 



[FIFTH SEEIES.] 



MARCH 1877. 



XXIV. On the Laws of the Passage of Electricity through 

 Gases. By G. Wiedemann*. 



SOME time since the author, in conjunction with Dr. 

 Riihlmann, made a series of experiments on the dis- 

 charge of electricity between spheres of metal in rarefied air. 

 The image of the discharge was reflected from a revolving 

 mirror fixed on the axis of a Holtz machine which supplied 

 the electricity. The reflected rays passed through a telescope, 

 the object-glass of which was divided vertically, like a helio- 

 meter, into two parts, one of which was displaced until the 

 image of one discharge seen in one half was brought into a 

 line with that of the next discharge seen in the other half. 

 The amount of displacement was measured. 



In all the experiments the pressure of the gas was so far 

 reduced that the discharge took place through the gas alone, 

 unmixed with any material particles from the electrodes. 



These experiments led to the following conclusions : — 



I. That the potential on the spherical electrodes, necessary 

 for effecting a discharge, is greater for the positive than for the 

 negative electrode. 



This result was obtained by measuring the time-interval be- 

 tween two consecutive discharges — (1) when one electrode 

 was charged with positive or negative electricity and the other 

 connected with the earth, (2) when both electrodes were con- 

 nected with the machine, but one was larger than the other. 



II. The quantity of electricity necessary fo reffecting a dis- 



* Communicated by W. Spottiswoode, F.R.S. (The original papers 

 will be found in Poggendorff's Annalen, vol. cxlv. pp. 235, 864, and 

 vol. clviii. p. 35.) 



Phil. Mag. S. 5. Vol. 3. No. 17. March 1877. M 



