upon the Electrical Discharge in Rarefied Gases. 131 



which remains the same in all cases, with the exception that the 

 diverse nature of the gases in the interior of the tubes affects in 

 many ways the pha;nomeua of colour. Tubes containing carbonic 

 acid, to adduce one more example, give a beautifully stratified 

 green light. The luminous atmosphere around the warmth- 

 pole is of a beautiful blue, and the envelope of light around it 

 again green. The surfaces of light into which the blue light 

 collects, under the influence of the magnet, are in nowise differ- 

 ent in form from those before described. 



37. The colour of the luminous atmosphere around the 

 warmth-pole, and of the surfaces in which it collects under the 

 influence of magnetism, is totally independent of the nature of 

 the electrodes. Three precisely similar tubes were taken, pro- 

 vided at their extremities with similar bulbs, into the middle of 

 which the platinum wires extended. The platinum wires were 

 prenously covered with- fused glass at the parts where they were 

 melted into their respective glass bulbs ; one of them was then 

 coated (galvanically) with gold, the second with silver, and the 

 third with copper. The phsenomenon presented under the in- 

 fluence of magnetism was perfectly the same on making each 

 of the ends of the three tubes, one after the other, the positive 

 electrode. 



38. Finally, a small sphere was melted on to the end of a 

 platinum wire*; and after covering all the rest of the wire with 

 melted glass for the sake of isolation, it was fused into a wider 

 tube, with the sphere as warmth-electrode. From this sphere aa 

 a centre the whole luminous atmosphere spread out, which, by 

 the action of magnetism, was concentrated, not, as before, to a 

 surface of light, but to a line of light, a briyhtly luminous mag- 

 netic curve. 



If the whole of the platinum wire serving as warmth-electrode 

 be isolated in the manner described, with the exception of sevei'al 

 single points, every such non-isolated place becomes a centre 

 of light, spreading out in all directions, which light is drawn 

 together by the magnet into the magnetic curve passing through 

 this point. Such a luminous magnetic curve corresponds to 

 every one of the points. If the platinum wire be not isolated, 

 every one of its points gives rise to radiant light, and we obtain 



* As it may be desirable for many purposes to form platinum wires 

 terminatiug in a s))here, I shall here mention the following sure and easy 

 method which I have for many years employed for this ])urpose. I take 

 three or more Grove's elements, according to the thickness of the wire, 

 and complete the circuit by means of mercury with the platinum wire as 

 warmth-jiolc. The point of the wire melts on coming into contact w ith the 

 surface of the mercury. The contact is [)rescrvcd by gradually advancing 

 the wire, from 1 to 2 inches of which are melted iu a few seconds, to a perfect 

 uphere. 



K2 



