in highly Rarefied Elastic Fluids. 253 



clerecl visible by the electricity which traverses it. The slow- 

 ness with which this rnist spreads affords an indication of 

 the small elastic force of the gas. It is probably in conse- 

 quence of the same cause that the gas which enters the tube 

 mixes so slowly with what was there before, as is rendered 

 evident by the sharp and narrow striee which appear in the new 

 portion of gas, while those in the original quantity of gas are 

 much wider and less well defined — a difference which can only 

 be due to the fact that the entering gas is not, at the moment 

 of entering the tube, as greatly rarefied as that which was already 

 there. Lastly, the fact that the narrowly striated gaseous column 

 is much wider when the gas which produces it enters near the 

 negative electrode than when it enters near the positive elec- 

 trode, is a proof that before the introduction of the additional 

 quantity of gas, the gaseous column which the tube already con- 

 tained was much more expanded in the neighbourhood of the 

 negative than in that of the positive electrode. Accordingly 

 the passage of a rapid succession of electric discharges through 

 a rarefied column of gas must produce in it, when the rarefaction 

 has reached a certain point (which varies with the nature and 

 therefore with the conductivity of the gas), first of all a consider- 

 able expansion of the gaseous matter surrounding the negative 

 electrode, and then, starting from this greatly expanded portion 

 of the column, a succession of alternate expansions and conden- 

 sations all the way to the positive electrode. It is very probable 

 that the same effect takes place when the gas is not rarefied suf- 

 ficiently for stratifications of the electric light to be produced. 

 But in that case the greater elastic force of the gas, combined 

 with the necessarily less rapid succession of discharges, allows 

 the condensed and expanded strata to return immediately to their 

 normal density^ and thus prevents this twofold condition from 

 showing itself; whereas, when the gas is less elastic and the 

 discharges follow each other more rapidly, the condition of ex- 

 pansion and contraction produced by a first discharge lasts until 

 a second discharge occurs, and is thus rendered permanent and 

 sensible. 



The transmission of electricity through a column of gas thu3 

 determines a movement of the particles of the gas; and this 

 movement seems to originate in an impulse driving them away 

 from the negative electrode. May not this effect be attributed 

 to the statical electricity with which the particles become charged, 

 and which increases their inherent repulsion ? It is well known, 

 and it is made visible by the luminous halos which surround the 

 negative knob and stem, that under equal tensions negative 

 electricity escapes more easily from metallic electrodes into the 

 surrounding rarefied medium than positive electricity. Conse- 



