the Nature of Spectra, 93 



Very hot spark discharges even might exert similar actions. 

 But we cannot hence infer that the hydrogen itself vanishes 

 or is transformed into a material of another nature. 



The above-described phenomena might result from several 

 causes. (1) The vaporized mercury may crowd the other 

 gases out of the hotter portions of the tube into the colder, so 

 that its own vapour alone is found in the path of the spark. 



(2) The phenomena depend on differences of temperature oc- 

 curring in the spark itself when the discharge passes through 

 gases mixed with mercury and also through pure gases. 



(3) They are conditioned by this — that whenever any two 

 gases are mixed, only one of them becomes luminous. (4) Mer- 

 cury particles are torn from the electrodes, and carryover the 

 electricity in disruptive discharges. (5) Mercury behaves 

 towards electricity essentially otherwise than hydrogen and 

 nitrogen. 



To test the first assumption the Geissler tubes were placed 

 vertically instead of horizontally. If this assumption had been 

 correct, the behaviour of the upper must then have been essen- 

 tially different from that of the under parts — which, however, 

 was not the case. A further argument against this assumption 

 is, that in tubes of equal width throughout the phenomena 

 were as well exhihited as in tubes with a capillary middle 

 piece. 



Secondly, that the disappearance of the lines is not condi- 

 tioned by differences of temperature in the spark itself, follows 

 from the fact that when the most different sources of electri- 

 city are employed (which produce very differently heated dis- 

 charges) it equally occurs, that it is also independent of the 

 nature of the electrodes, and that it is exhibited in the wide as 

 well as in the narrow portions of the Geissler tubes (in which 

 the temperatures differ considerably). Further, if we view in 

 the rotating mirror the discharges of a Holtz machine that 

 take place in a Geissler tube, the intervals between them after 

 the heating, when the mercury-lines appear, are not essentially 

 other than at the ordinary temperature, provided only that the 

 pressure in the Geissler tube has not varied during the expe- 

 riment — which it was easy to secure by keeping it constantly 

 connected with the air-pump. Since the intervals do not vary, 

 equal amounts of electricity pass in equal times, and the tem- 

 peratures of the incandescent particles of gas will not be very 

 different. 



Thirdly, in order to establish that the appearance of the 

 spectrum proper to nitrogen was not prevented by the addi- 

 tion to it of any considerable quantity of any gas or vapour 

 whatever on the passing of the electric spark, some iodine was 



Phil. Mag. S. 5. Vol. 7. No. 41. Feb. 1879. I 



