in highly Rarefied Elastic Fluids. 247 



§ 2. Investigation of the Stratification of the Electric Light. 



It is well known that when the elastic force of a gas through 

 which an electric discharge is passing is diminished to a certain 

 point the discharge becomes stratified ; that is, it breaks up into 

 alternate dark and light slices. The stratification begins with 

 the appearance of a lew slight stride near the positive electrode; 

 (hen gradually, as the elastic force is diminished, the discharge, 

 which is at first very narrow, expands and the striae become 

 broader. Soon afterwards a dark space appears separating the 

 luminous column from the negative electrode, which latter is itself 

 surrounded by a bluish atmosphere. This atmosphere continues 

 to expand, and the dark space to get longer, in proportion as the 

 rarefaction of the gas increases. 



The pressure of the gas must be the more diminished, in order 

 to obtain the stratification of the electrie light, the greater the 

 resistance which the gas offers to the transmission of electricity. 

 Thus, with hydrogen, even with a pressure of 18 millimetres, the 

 electric discharge, which as yet consists merely of a narrow rose- 

 coloured vein, of 8 or 4 miilims. diameter, is seen to separate 

 into sharply defined circular slices, alternately dark and bright, 

 and J millim. in thickness. These strise, which are at first 

 most distinct at the positive electrode, appear afterwards through- 

 out the luminous vein, whatever may be its length ; and as the 

 pressure diminishes, the discharge spreads out, so as to occupy 

 the whole width of a tube 5 centims. in diameter; and at the 

 same time the thickness of the alternate dark and luminous slices 

 increases, to such an extent that under a pressure of 2 miilims. 

 it is about 5 miilims. These slices are annular, as I convinced 

 myself by closing one end of the tube which contained the rare- 

 fied gas by a flat plate of glass, which allowed the inside of the 

 tube to be seen throughout its whole length. 



From the time that the strise begin to show themselves, a 



He obtained the metallic vapours, through which he ^passed the discharge 

 of a RuhmkorfF's apparatus, by placing pieces of the metal upon a sheet of 

 iron enclosed in an exhausted receiver and heated to redness by a galvanic 

 current. But, with the exception of zinc and cadmium, he did not work 

 with the same metals as myself; and, with regard to the less volatile metals 

 in particular, his experiments were limited by the process which he em- 

 ployed for heating being less powerful than the one I used. Moreover the 

 object of his experiments was quite different from mine : he did not occupy 

 himself with the determination of the relative conducting- powers of me- 

 tallic vapours ; and this I consider to be the most important part of this por- 

 tion of my investigation. I am, however, none the less ready to acknow- 

 ledge M. Faye's priority as to the fact of the transmission of electricity 

 through metallic vapours. 



