1895.] On the Spectra of Argon. 289 



of argon. After the nitrogen had been absorbed by the spattered 

 platinum this pressure of argon would be near the point of non-con- 

 duction. 



In all cases, when argon has been obtained in this manner, the 

 spectrum has been that of the blue-glowing gas. It is not improbable, 

 and I understand that independent observations have already led 

 both the discoverers to the .same conclusion, that the gas argon is 

 not a simple body, but is a mixture of at least two elements, one of 

 which glows red and the other blue, each having its distinctive 

 spectrum. The theory that it is a simple body has, however, support 

 from the analogy of other gases. Thus, nitrogen has two distinct 

 spectra, one or the other being produced by varying the pressure and 

 intensity of the spark. I have made vacuum tubes containing 

 rarefied nitrogen, which show either the fluted band or the sharp 

 line spectrum by simply turning the screw of the make-and- break, 

 exactly as the two spectra of argon can be changed from one to 

 the other. 



I have prepared tubes containing other gases as well as nitrogen at 

 different pressures, and have examined their spectra both by eye ob- 

 servations and by photography. The sharp line spectrum of nitrogen 

 is not nearly so striking in brilliancy, number or sharpness of lines 

 as are those of argon, and careful scrutiny fails to show more than 

 one or two apparent coincidences between lines in the two spectra. 

 Between the spectra of argon and the band spectrum of nitrogen 

 there are two or three close approximations of lines, but a projection 

 on the screen of a magnified image of the two spectra partly super- 

 posed will show that two at least of these are not real coincidences. 



I have looked for indications of lines in the argon spectra corre- 

 sponding to the corona line at 531*7, the aurora line at 557*1, and the 

 helium line at 587*5, but have failed to detect any line of argon suffi- 

 ciently near these positions to fall within the limits of experimental 

 error. 



I have found no other spectrum-giving gas or vapour yield spectra 

 at all like those of argon, and the apparent coincidences in some of 

 the lines, which on one or two occasions are noticed, have been very 

 few, and would probably disappear on using a higher dispersion. 

 As far, therefore, as spectrum work can decide, the verdict must 

 be that Lord Rayleigh and Professor Ramsay have added one, if not 

 two, members to the family of elementary bodies. 



