178 Prof. G. Wiedemann on the Laws of the 



negative electrode a water resistance is interposed ; its extent 

 increases therefore with, the quantity of electricity conducted 

 to the electrode in a given time ; meanwhile, except with very 

 great quantities of electricity, the negative electrode is illu- 

 minated throughout. At the positive electrode the same in- 

 fluences only produce a greater or smaller extension of the 

 discharge on the electrode. It is smaller in proportion to the 

 supply of electricity. 



According to the opinion expressed above, it might be 

 thought that, starting from the negative electrode (sup- 

 posed to be directly connected with the source of electricity), 

 not only the gas molecules which are in immediate contact 

 with it, but also those that are at a distance, receive a 

 distribution of electricity diminishing with the distance. If 

 the electrode is opposite to a glass wall which is eventually 

 put to earth externally, this direct induction from the elec- 

 trode extends yet further. With an increasing charge the 

 portions of gas approach nearer to the electrode, so far as the 

 elastic properties of the gas permit. In front of them appears, 

 for the moment, a rarefied space. If at the commencement of 

 the discharge the negatively charged portions of gas which 

 touch the electrode are driven away, they impart their charge 

 to the following set of molecules ; then either they, or other 

 portions of gas in succession, charged with divided electricity 

 betake themselves to the electrode, where they neutralize the 

 electricity of the opposite name and become negatively 

 charged. In consequence of this, not only is the electrode 

 much heated, but a great velocity is imparted to the particles. 

 Wherever this communication between the electricities takes 

 place, whether between the electrode and the particles, or 

 between the particles themselves, the blue halo must appear and 

 eventually spread itself as far as the opposite glass wall. The 

 heating of the electrode is therefore immediately connected 

 with its appearance. This sort of discharge will last so long 

 as the charge of the electrode is powerful enough to impart 

 to the particles a velocity corresponding to the pressure. 



If the negatively charged electric particles in succession 

 leave the neighbourhood of the electrode and traverse the 

 rarefied space in front of them, there ensue few, if any, en- 

 counters with other molecules ; on the contrary, the particles, 

 in consequence of their mutual electric repulsion, occupy a 

 larger space, and their temperature and brightness appear, 

 therefore, less than where they are pressed close to the elec- 

 trode ; so that the space will appear either dark, or illumi- 

 nated only by a dull and cloudy light. Only when the 

 negatively charged molecules strike the uncharged, and charge 



