120 Pi-of. Pliickei- on the Action of the Magnet 



determines uic to complete my foi-mer communications ; in doing 

 so I shall trespass as little as possible upon investigations to be 

 published subsequently. 



2. The first two tubes, which M. Geissler prepared according 

 to direction, contained mercury and atmospheric air in the 

 highest possible state of rarefaction. At my suggestion, re- 

 sulting from former trials, instead of air, the vapour of an sethe- 

 rial oil, hydrogen, and phosphorus were employed, and the tubes 

 Mere widened at one part. The mercury also was removed from 

 the tubes, but their evacuation was still performed by its means. 

 The two tubes containing the last-named substances, hydrogen 

 and phosphorus, still continue to give a beautiful effect with 

 the gi'eatest certainty. M. Geissler, however, afterwards tried 

 many other gases, both simple and compound, altering at the 

 same time the shape of the tubes in various ways. In most 

 cases it has hitherto been difficult to say with certainty what 

 gases are contained in the Geissler tubes. Even on testing one 

 of the first of these tubes which contained the vapour of an 

 fetherial oil, an immediate alteration in the phsenomenon ap- 

 peared, owing to the decomposition of the vapour. This elec- 

 trolysis of dilute compouad gases received complete verification 

 in subsequent cases. In tubes containing hydriodic acid, the 

 iodine is gradually deposited. In highly rarefied gases this 

 electrolysis by the electric stream, as it becomes finely divided, 

 often manifests itself suddenly by a remarkable alteration of 

 colour. Examples of this were furnished by tubes containing 

 phosphoretted hydrogen and sulphurous acid. The laws of the 

 electrolysis brought about by the spark of Ruhmkorff's appa- 

 ratus may, however, be traced in gases and vapours of ordinary 

 density. 



3. The metal composing the electrodes, especially the negative 

 one, is transferred to the glass of the tube. This is the case 

 even with platinum electrodes ; and the blackening of the tube 

 in the neighbourhood of the warmth-pole (the negative pole) is 

 principally attributable to the combination of the platinum with 

 traces of other substances present in the tube. 



4. In the different Geissler's tubes the light appears of all 

 kinds of colours, often of a very intense nature, and on analysis 

 with the prism yields variously modified spectra. The descrip- 

 tion of these colours, especially the more delicate ones, is the 

 more difficult, inasmuch as the impression they produce upon the 

 eye depends upon the external illumination, and the same colour 

 may, for instance, appear bright violet or rosy red, according as 

 it is viewed by weak daylight or by the light of a candle. 



5. The dark bands first observed by Kuhmkorff and Quet in 

 the electrical egg appear in Geissler's tubes of the most varied 



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