On Electric Discharges through Rarefied Gases. 353 



times reflected, whoso position is the same as that part of the 

 spectrum A\4iich passes with minimum deviation*. I am in- 

 formed by Captain Abney that the bases of Herschel's prisms 

 were polished, which is so far in favour of this view. Never- 

 theh'ss I feel great hesitation in suggesting such an exphma- 

 tion, and only do so in default of any other. I should be very 

 glad if some other experimenter could be induced to under- 

 take an examination of the subject, and would willingly fur- 

 nish for comparison specimens of the spectra that I have my- 

 self obtained, 



Terling Place, Witliam, 

 September 1877. 



XL VIII. Preliminary Communication on Electric Discharges 

 through Rarefied Gases. By EuGEN GrOLDSTElNf. 



DURING an investigation on luminous discharges through 

 gases, which I was able to make in the Laboratory of 

 the Berlin University, I have arrived at the following results. 



1. We cannot maintain any more the distinction which has 

 been drawn between the positive and negative lights ; nor is 

 it probable that the positive discharge is analogous to the 

 metallic or electrolytic conduction, as has been stated. Posi- 

 tive and negative light are of the same kind ; and it is possible 

 to connect them by a continuous series of intermediate stages. 

 I retain, however, for the present the name negative light 

 for the phenomenon in which the properties which have been 

 hitherto supposed to be characteristic of the light at the nega- 

 tive pole are prominently brought forward. 



I have been able to give, by a suitable experimental disposi- 

 tion, all properties which are supposed to belong to the nega- 

 tive light only, to the positive discharge, with the sole excep- 

 tion of the peculiar stratification of the negative light. 



Such properties are, for example, colour and spectrum of 

 the negative light, its behaviour in the magnetic field, the 

 power to produce fluorescence, the formation of the dark 

 space, (fee. 



2. I call the space in a vacuum-tube vrhich is situated 

 towards the negative pole the negative space. My results are, 

 then, as follows: — 



The properties of the discharge between the positive pole 

 and the dark space depend on the alteration in the cross 

 section of the conducting gas. If the cross section increases 



* Helmholtz, Physiologische Optik, p. 263. 



t Translated by Dr. Arthur Schuster from a separate copy of the Mo- 

 natshericJde der Akachmie der JVissenschaften zu Berlin^ May 4, 1876. 



Fhil. Mag, S. 5. Vol. 4. No. 26. >ov. 1877. 2 A 



