410 Prof. Pliicker on the Electrical Discharge 



51. What are the conditions for the formation of that mag- 

 netic light which has hitherto only been observed at the nega- 

 tive electrode, being thei-e sharply separated from that light 

 which forms the electric light-current, and which suffers by the 

 magnet the deflection of such a current, that is, an electro-mag- 

 netic one ? What is the diflerence between these two kinds of 

 light, upon which the magnet exerts so different an action ? 



Small particles of platinum are generally torn off from the 

 negative platinum electrode and deposited upon the internal sur- 

 face of the glass bulb enclosing the electrode*. A consequence 

 of this is, that this bulb becomes gradually blackened, and after 

 a long-continued action, the bulb, if not too great, becomes coated 

 internally with a beautiful metallic mirror. By chemical ana- 

 lysis we may prove the presence of platinum in the deposit. It 

 is clearly most natural to imagine the magnetic light to be formed 

 by the incandescence of these platinum particles as they arc torn 

 from the negative electrode. We must not, however, forget the 

 fact that the bulbs do not blacken in all cases. Even in such 

 cases (as, for instance, in tubes containing fluoride of boron) 

 where the magnetic light is very beautiful, and the influence of 

 the magnet upon it very great, no deposit upon the bulb is ob- 

 servable, although the action goes on for a long time. The 

 deposit has a very different appearance according to the nature 

 of the gas in the tube. The nature of the gas has, further, an 

 effect upon the warming of the negative electrode, which, under 

 circumstances otherwise identical, sometimes glows brightly, and 

 sometimes not at all. The radiation of luminous particles of 

 platinum must appear especially strange in the case where the 

 spark of a very moderate-sized electrical machine is discharged 

 through the tube (42), and where, under ordinary circumstances, 

 an elevation of temperature of the negative electrode would be 

 scarcely perceptible. 



The increased temperature of the negative electrode is com- 

 municated to the bulb surrounding it, probably principally by 

 means of the platinum particles projected from the pole. 



.52. It would scarcely require a special experiment to prove that 

 the bulb would only be blackened at the place where the disc of 

 light came into contact with its internal surface, if a fresh tube 



side of this arch was the brightest and the most shari)ly defined, and touched 

 the vvu-e above the middle point between the two armatures. This arch re- 

 mained unmoved and unchanged, on shpping the tube along, in the direc- 

 tion of its length, until the extremity of the electrode passed beyond the 

 middle between the two armatures. The phfcnomenon then underwent a 

 change, which need not be here further considered. 



* I have never observed a tendency of these atoms to move towards the 

 other electrode. 



