THE PROPAGATION OF ELECTRICITY. 179 



that we sboixld ascribe the slowness with which the mixture of the gas which 

 is entering the tube with that ah-eady present is effected — a slowness which is 

 manifested by the circumstance of the definite and narrow strice appearing in 

 the new portion of gas, while in the old the striae are much larger, and by no 

 means so distinctly defined — a phenomenon which can only proceed from the 

 former not being, at the moment when it enters the tube, so much dilated as the 

 gas which was already there. In fine, the fact that the gaseous column with 

 narrow striai is much larger when the gas which produces it enters on the side 

 of the negative electrode than when it enters on that of the positive, is a proof 

 that, before the new introduction of gas, the gaseous column already in the tube 

 was much more dilated in the neighborhood of the negative electrode than on 

 the side of the positive. So, then, the passage of the electric discharges very 

 rapidly succeeding one another across a rarefied gaseoi;s column would pro- 

 duce therein, when the rarefaction had reached a certain degree variable with 

 the nature, and consequently with the conductibility of the gas, first, a consid- 

 erable dilatation of the gaseous matter around the negative electrode, and next, 

 beginning in this dilated portion of the column, a succession of alternate con- 

 tractions and dilatations as far as the positive electrode. It is highly probable 

 that the same effect takes place when the gas is not sufficiently rarefied for 

 producing stratification of the electric light. But in that case, the greater 

 elastic- force of the gas, joined with the necessarily less rapid succession of the 

 discharges, allows the immediate return of the contracted and dilated strata to 

 their state of normal density, and thus prevents that double state from mani- 

 festing itself; while Avh en the gas is less elastic, and the discharges succeed one 

 another more rapidly, the state of dilatation and contraction of successive strata 

 produced by a first discharge still subsists when a second arrives, the result 

 being that it becomes sensible. 



The transmission of electricity, then, through a gaseous column occasions a 

 movement in the particles of gas, and that movement seems to be an impulse 

 emanating from the negative electrode. Might not this effect be attributed to 

 the static electricity with Avhich the molecules are charged, and which would 

 augment their constitutive repulsion 1 We know, and it is seen by the lumi- 

 nous aureoles which surround the negative ball and rod, that, at an equal tension, 

 the negative electricity issues more readily than the positive from its metallic 

 electrodes in order to penetrate into the rarefied ambient medium. Hence, the 

 portion of that medium nearest to the negative electrode must be more charged 

 with static (negative) electricity than is (with positive) the portion of the rare- 

 fied gas near the positive electrode ; it is not, then, surprising that the repulsion 

 of the gaseous molecules, and consequently the rarefaction of the gas, should be 

 greater in the first of these two portions than in the second.* Now, why does 

 negative electricity diffuse itself more easily than jiositive under the same con- 

 ditions of intensity, magnitude, and position of electrodes, nature and rarefac- 

 tion of the ambient medium 1 Here is the mystery, or at least a point of most 

 interesting consideration as regards the theory of electricity. 



^ III.— PARTICULAR PHENOMENA PRESENTED BY DIFFERENT PARTS OF 

 THE STRATIFIED ELECTRIC CURRENT. 



The gaseous column traversed by the electric current is composed, as we 

 have said, when it has been brought to a certain degree of rarefaction, of strata 

 alternately dilated and contracted, with an obscure space greatly dilated in the 

 neighborhood of the negative electrode. The more dilated parts of the column 

 offering less resistance to the transmission of electricity must remain obscure. 



* Tbe fact that the electricity of tension is more easily propagated around the negative than 

 around the positive electrode may be readily verified by experiment, as well as the permanent 

 state of electric tension of the gaseous column during the passage of the electric current, what- 

 ever may be the rarefaction of the gas. 



