H. V. Gill — Electric Discharge in Geissler Tubes. 415 



charge, as we had anticipated. Near the negative terminal the 

 lines became indistinct and often were not observed at all. It 

 is not necessary to dwell on the results, as they are sufficiently 

 explained by what has already been said regarding the nature 

 of the spark. 



Having proved that there are gas waves in the Geissler tube, 

 we can deduce the existence of the stratified discharge. Since 

 the gas is strongly electrified the discharge takes place between 

 the molecules (or as some hold, between the atoms); these inter- 

 molecular discharges produce the illumination in the body of 

 the gas. Add now the effect of waves in the gas. The gas at 

 a condensation will be in a different condition from that at a 

 rarefaction. When the molecules are crowded together at a 

 condensation the number of inter-molecular discharges will be 

 very much greater than at a rarefaction. There will hence be 

 a greater illumination at a node — this is a stratum ; but as the 

 state of condensation at a node is intermittent the illumination 

 will be so too. Therefore, remembering that the strata are 

 only relatively bright, and that they are not places of constant 

 brightness, we at once deduce their existence from the presence 

 of the waves caused by the electric discharge. And as this 

 visible effect would only be evident under special circumstances 

 we see how they are only observed within certain limits of 

 pressure, the cause being always present. Thus the identity of 

 the stratified discharge with the ordinary spark discharge seems 

 to be established. 



As has been proved by our experiments, the waves in the 

 gas ought to exist all along the tube, even near the negative 

 terminal; their absence as strata being due to mere local influ- 

 ence of the negative pole. In connection with this an experi- 

 ment of De la Rive's is of interest. Referring to the effect of 

 introducing a small amount of gas into the tube during the 

 stratified discharge, he says :* " We begin by reducing the 

 pressure to 2 mm so that the phenomenon of stratification may 

 be as pronounced as possible. We then cause a small amount 

 of hydrogen to enter the tube ; if the gas enters at the end 

 near the negative electrode, we see at once strata formed in the 

 obscure space which are of a beautiful rose colour. . . . They 

 are propagated gradually in the tube and unite with the original 

 strata; ... on arresting the introduction of the gas we see the 

 luminous column slowly leave the negative electrode and take 

 by degrees its primitive appearance." This tends to show that 

 the dark space is due to the comparative absence of gas near 

 the negative electrode, just as in our first experiments in air 

 the powder is driven away near the spark. Both facts are thus 

 probably due to the same cause. 



* Loc. cit. p. 451. 



Am. Jouk. Sci.— Fourth Series, Yol. V, No. 30.— June, 1898. 

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