144 THE ROYAL SOCIETY OF CANADA 



a brass tube 35 cm. long and 1.5 cm. in diameter, having quartz 

 windows 1 . 2 cm. in thickness securely held by brass caps screwed to 

 the tube. The source of radiation was the spark between aluminium 

 terminals under distilled water, which gave a continuous spectrum 

 between the wave-lengths previously mentioned. The light from 

 this spark was passed through the absorption tube filled with the gas 

 and brought to a focus on the spectrograph slit. 



The gas in the absorption chamber consisted of a mixture of 

 80 per cent, argon and 20 per cent, nitrogen at a pressure of 128 

 atmospheres and was obtained from the Canadian Sunbeam Lamp 

 Company of Toronto. The equivalent argon pressure was 102.4 

 atmospheres, and as it was known from previous work that nitrogen 

 at a pressure of 140 atmospheres was transparent in this region, the 

 effect of the nitrogen in the tube was neglected. The photographic 

 plates were Wratten panchromatic, as in the previous experiments 

 and the time of expjosure was one and three-quarters hours. There 

 was no indication of any appreciable or visual absorption between 

 the wave-lengths X = 7000 Â.U. and X = 2150 Â.U. 



IV. Summary 



1. The absorption spectrum of ionized argon gas at pressures of 

 155, 5, and 2 mm. of mercury has been investigated between the wave- 

 lengths X = 7000 Â.U. and X = 2150 Â.U. No absorption was detected. 



2. The absorption spectrum of argon gas at an equivalent 

 pressure of 102.4 atmospheres has been studied in the same region. 

 The gas at this pressure has been found to be transparent between 

 the wave-lengths previously mentioned. 



In conclusion the author wishes to express his sincere thanks to 

 the members of the Advisory Council for Scientific Research, and 

 particularly to Professor J. C. McLennan, F.R.S., who suggested 

 these researches and under whose direction they were carried out. 

 The author also desires to express his gratitude to Miss M. L. Clark, 

 who assisted in the purification of the gas and in filling a number of 

 the tubes. 



Physical Laboratory, 

 University of Toronto. 

 May 15th, 1922. 



