The Multiple Spectra of Gases. 135 



had been attracted. Hence, amongst the rays deflected by the 

 magnet there are some endowed with photographic action. 



In addition, I tried to investigate how the photographic 

 action inside the tube varies with the variation of the rare- 

 faction. 



The result of the experiments proved that such action takes 

 place even when all the conditions that we judge to be 

 ordinarily connected with the production of the kathodic rays 

 are not satisfied. 



Beginning with the internal pressure of 3/10 of a milli- 

 metre, at which the tube is filled with a white-violet light that 

 ends at the two electrodes, where from time to time little 

 sparks are visible, the photographic action increases at first 

 rapidly with the rarefaction, and then, from 1/100 of a milli- 

 metre onwards, much more slowly. 



Finally, to eliminate the doubt that the photographic action 

 inside the tube was due to an electric effluvium between 

 the paper and the metallic cylinder*, I surrounded the latter 

 with a thimble of brass-wire gauze connected to a copper 

 wire dipping into the mercury of the pump, which, in its turn, 

 was put in connexion with the ground. 



All the films showed on development a darkening of the 

 same order of intensity as that which was produced without 

 the metallic screen, while the shadow of the whole gauze 

 remained well delineated on the film itself. 



While these experiments point to facts noteworthy in 

 themselves, they lead us to conclude that Rontgens rays are 

 already existing inside the tube as well as those studied, by Lenard. 

 The ones would pass better than the others through the walls. 

 Hence they alone would pass out if the tube were of a somewhat 

 thick glass. 



XX. The Multiple Spectra of Gases. 

 By John Trowbridge and Theodore Wm. Richards |. 



IN a recent paper upon the spectra of argon % we have showm 

 that the two different spectra of this gas are dependent 

 primarily upon the electrical conditions which cause the gas 

 to glow. The continuous discharge of a high-tension accu- 

 mulator through the gas produces the red spectrum, while the 

 discharge of a condenser, provided that its oscillations are 



* This was already sufficiently contradicted by the fact that the im- 

 pression came out enormously stronger on the face turned towards the 

 kathode. 



f Communicated by the Authors. J Suprd, p. 77. 



