254 Prof. Be la Rive on the Propagation of Electricity 



quently the portion of this medium which is near the negative 

 electrode must become more highly charged with (negative) sta- 

 tical electricity than that portion of the rarefied gas which is 

 near the positive electrode does (with positive electricity); it is 

 therefore not surprising that the repulsion of the gaseous mole- 

 cules, and consequently the rarefaction of the gas, should be 

 greater ia the former portion than in the latter*. Now why 

 does negative electricity diffuse itself more easily than positive, 

 under like conditions as to tension, as well as size and position 

 of the electrodes and nature and state of rarefaction of the sur- 

 rounding medium ? This is a mystery, or at least a very inter- 

 esting point to investigate in "connexion with the theory of 

 electricity. 



§ 3. Special Phenomena presented by the different parts of the 

 Stratified Electric Discharge. 



The gaseous column traversed by an electric discharge is com- 

 posed, as we have said, when it has been brought to a certain 

 degree of rarefaction, of alternate expanded and condensed strata, 

 with a greatly rarefied dark space near the negative electrode. 

 The more expanded parts of the column, since they oppose less 

 resistance to the passage of the electricity, must remain dark ; 

 while the more condensed parts, possessing a lower degree of 

 conductivity, must become heated and luminous even when all 

 parts are traversed by the same discharge. We ought to have 

 here a phenomenon absolutely analogous to that which is pro- 

 duced when a chain formed of wires of the same length and dia- 

 meter, alternately of silver and of platinum, is placed in the cir- 

 cuit of a galvanic battery : although they all transmit the same 

 current, the platinum wires, having a greater resistance, become 

 heated and even incandescent, while the better-conducting silver 

 wires remain cold and dark. 



In order to prove that the part which remains dark does in 

 reality offer less resistance to the passage of electricity than the 

 luminous portions of the stratified column, I employed two small 

 disks of platinum, each of them fixed by a point in its circum- 

 ference to the extremity of a platinum wire enclosed in a glass 

 tube, in such a way that they were kept parallel to each other at 

 a distance of 3 centims. The two disks were firmly fastened in 

 proximity to, but very carefully insulated from, each other, and 



* The fact that electricity of tension spreads more readily round the 

 negative than round the positive electrode can easily be proved experimen- 

 tally — as well as the state of permanent electric tension of the gaseous 

 column during the passage of the electric discharge, whatever may be the 

 degree of rarefaction of the gas. 



