Passage of Electricity through Gases. 171 



The similar movements proceeding from the two electrodes 

 meet in one part of the tube, where the balancing of the 

 opposed electricities of the now mutually attractive last mole- 

 cules takes place. During this process the velocity of the 

 single gas-molecules may become so great as to render the gas 

 luminous. Meanwhile the action effected by the union of the 

 opposed electricities in two consecutive molecules will be com- 

 pensated by the division of the electricities in each molecule. 



If the gas be capable of electrolytic decomposition, the 

 movements of the gas-molecules, as above described, may be 

 connected with a separation, dispersion, and reunion of their 

 atoms, similar to other electrolytic processes, as shown by the 

 experiments of Perrot*. 



If the electrodes in a glass tube be so far apart that their 

 mutual influence may be neglected, the phenomena become 

 more complicated, because the sides of the tube may become 

 charged from the electrodes. Although with the apparatus 

 above described the so-called "positive discharge" always 

 passes through the entire length of the capillary tube, it is 

 only when the negative electrode is put to earth that the 

 whole tube receives a positive charge, diminishing of course 

 in strength with the distance from the positive electrode. 



With insulated electrodes it is only in part positively 

 charged ; but when the positive electrode is put to earth it is 

 negatively charged from the negative electrode in its entire 

 length, with diminishing intensity. This free electricity, as we 

 know, holds the opposing electricity on the outer surface of 

 the glass, while that of the same name becomes more or less 

 dispersed. The electricity distributed upon the inner side of 

 the glass tube may have some effect upon the tension at the 

 electrodes. It has also some influence upon the velocity and 

 direction of the movement of the gas-molecules, as is very 

 clearly shown by experiments with the larger glass tube. 

 The principal impulse, however, appears, as in the free space, 

 to proceed from the electrodes themselves ; for instance, if 

 the positive electrode be put to earth, the fall of electricity 

 measured from the negative electrode in a tube of the length 2 

 is indeed only half as great as in a tube of length 1 ; but yet 

 the production of heat per unit of length in both tubes is 

 nearly equal. 



The transmission of motion from gas molecule to gas 

 molecule occasioned by the partition of electricity in the 

 tubes should, if we neglect the communication of heat to the 

 sides, take place in accordance with the laws of elastic 

 impact. If in this case the discharge proceeds from a wider 

 * Cf. Gatvanismus, 2. Aufl. Bd. ii. S. 412. 



