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XXII. On the Problems of Temperature Radiation of Gases. 

 (Paper C.) By Megh Nad Saha, D.Sc, Lecturer in 

 Physics and Applied Mathematics, University College of 

 Science, Calcutta *. 



§1- 



ri^HE object o£ the present paper is to discuss and examine 

 _L the present-day position of the question of temperature 

 radiation of gases. The problem before us is, whether by 

 simply heating a quantity of gas confined within a closed 

 vessel (say, a silica or a graphite tube), it is possible to make 

 the gas emit its characteristic line-radiation. The experi- 

 mental results on this subject are somewhat conflicting, 

 and for different elements are widely divergent. While 

 Pringsheim and others f found that permanent gases like 

 H 2 , He, Ne, A, N 2 , 2 , etc., remain non-luminous even at 

 the highest temperatures which can be commanded in the 

 laboratory, it is known that vapours of many elements easily 

 become luminous at moderate temperatures. Such, for 

 example, are the vapours of I, Br, As ; S, Se, Sb, and other 

 metalloids. If w r e take the tube-furnace spectra of King J 

 to be cases of pure temperature-radiation, we have to admit 

 that at temperatures varying from 2000° to 3000° K, most 

 of the alkalies, the alkaline earths, thallium, iron, vana- 

 dium, etc., can be made to emit their line-spectra. Gibson § 

 obtained the green line of thallium by simply heating the 

 element contained in a quartz tube. But the conclusion 

 drawn by him — that the intensity of the green line is the 

 same as that of the black body-spectrum at this particular 

 wave-length — is entirely wrong. He placed the quartz tube 

 within a black-body chamber heated to about 1200° C, and 

 observed that the continuous spectrum from the black body 

 was crossed by a black absorption line corresponding to the 

 green emission line. But this black line faded away as soon 

 as the thallium vapour took up the temperature of the 

 enclosure. From this he concluded that the emission of the 

 green line had just become as intense as that of the black 

 body at the same part of the spectrum. But the conclusion is 

 erroneous, for substances in temperature equilibrium within 

 a black body enclosure would all emit like a black body, and 

 the experiment proves nothing but this simple property of a 

 black-body enclosure. 



* Communicated bv the Author. 



t Pringsheim, Verh. d. Deutsch. I'hys. Gesettschaft, 1903. Wood, 

 Phys. Zeits. viii. (1907), and other papers. 



X King, Astro. Journal, vols, xxviii., xxxiv., xxxv., xxxvii. 

 § Gibson, Phys. Zeits. xii. pp. 1145-1148 (1911). 



