32 Electrical Researches by Be la Rive and Gassiot. 



two millimeters, an attentive examination of the obscure portion 

 reveals a pale light, sharply divided fronr]the luminous stratified 

 column of which it is the prolongation." 



M. de la Eive goes on to state the effect of introducing an 

 additional quantity of gas, corresponding to an increase of a 

 quarter or a half of a millimeter pressure. If the introduction 

 takes place on the negative side, annular rose-coloured striations 

 of the same diameter as the column of the discharge appear 

 in the dark space. They gradually propagate themselves 

 through the tube, and entangle* themselves with the primitive 

 striations, which are much broader and less defined. When 

 the supply of fresh gas is stopped, the luminous column slowly 

 removes itself from the negative electrode, and soon regains 

 its primitive appearance. Introducing the gas at the posi- 

 tive electrode, gives rise, in lieu of strias occupying all the 

 breadth of the tube, to a brilliant jet of very small diameter 

 (two or three millimeters), advancing along the axis of the tube 

 in " the relatively obscure interior of the luminous column, 

 which immediately occupies all the black space in the vicinity 

 of the negative electrode." These experiments M. de la Rive 

 considers to confirm the opinion of M. Riess, that the stratifi- 

 cations are purely mechanical phenomena, resulting from the 

 alternate contractions and expansions produced in the rarefied 

 fluid by the discontinuous character of the electric discharge. 

 He adds that this is shown by the employment of a manometer 

 in connection with the tube, when oscillations varying from 

 ^ to £ of a millimeter reach a maximum of amplitude, at 

 the moment when the gas reaches the degree of rarefaction 

 at which the striation appears. 



In further explanation, M. de la Rive observes that in the 

 rarefied column those bands which are the best conductors 

 remain dark, while those which offer most resistance become 

 luminous ; just as in the case of a chain of alternate links of 

 platina and silver, the former become incandescent, while the 

 latter remain cold. To prove this experimentally, he placed in 

 the tube two small disks of platiua, so that one should be im- 

 mersed in a dark space and the other in a light one when the 

 discharge was made. These disks acted as "sounds," and 

 wires connected with them afforded a weak current from the 

 dark spares, and a stronger one from those which were luminous. 

 He also found a difference of temperature in the two portions of 

 the discharge. 



"When a long tube containing hydrogen, at a pressure of 

 right millimeters, is placed axially or equatorially between the 

 poles of a powerful eleotro-magnet, the conducting power of 

 the medium diminishes from 30' to 1(T if the dark space is near 



* En B'cm-liL'vrlrant. 



