in highly Rarefied Elastic Fluids. 243 



directions, which occurs under these circumstances. But several 

 physicists, and particularly Mr. Gassiot, have obtained this phe- 

 nomenon by means of the electricity of the ordinary electrical 

 machine, and still better with that of a battery of high tension, 

 in which cases there could be discharges and currents in one di- 

 rection only. 



Mr. Gassiot has found, by studying these strise in a great 

 number of tubes containing vapours or gases more or less rare- 

 fied, that their number, colour, form, and mutual position depend 

 upon the degree of rarefaction of the elastic fluid and upon the 

 power of the battery. If a column of distilled water, the length 

 of which can be varied by bringing closer together or separating 

 to a greater distance two platinum wires which dip into it, is in- 

 troduced into the circuit of the battery, all the above-mentioned 

 variations in the stratification of the electric light can be pro- 

 duced in one and the same Geissler's tube, by altering in this 

 way the total resistance of the circuit. These appearances vary 

 so regularly with the amount of tension, that they may serve to 

 indicate the degree of tension in a closed circuit, just as the di- 

 vergence of the gold-leaves connected with the poles of the bat- 

 tery indicates the tension when the circuit is open. 



Before passing to the more particular examination of this stra- 

 tification of the electric light which is the special object of this 

 investigation, I will add a few words more about the general 

 phenomenon of the propagation of electricity by gaseous media. 



In 1863 I made some preliminary researches upon the con- 

 dncting-power of some of the gases, and more particularly of 

 hydrogen, nitrogen, and atmospheric air; I perceived the great 

 superiority in this respect of hydrogen to the other gases ; and 

 I showed that, when brought to such a degree of rarefaction that 

 their conductivity was near its maximum, columns of these three 

 gases obeyed the same laws as the best conductors, with reference 

 to the influence of their length and diameter upon the intensity 

 of the electricity transmitted. Since then, M. Morren has pub- 

 lished* the results of a careful examination of this question, and 

 has given for several gases the pressure at which each of them 

 possesses its maximum conductivity. 



But, in order to complete this investigation, there are still 

 some determinations wanting, and some points which call for 

 further examination, particularly the influence of temperature, 

 and that of the presence of different vapours in the rarefied gases. 

 This is a subject with which I am at present occupied, and I will 

 make known the results when the new researches which I hope 

 to take in hand immediately are finished. 



For the present, I will confine myself to stating here some 

 * Ann. de Chlm. et dePliys. ser. 4. vol. iv. p. 325. 

 R2 



