Dispersion of Carbon Dioxide in the Infra-red Region. 737 



In the above columns, the first number is n, the second 

 A — ?i, the third log ( A — n), the fourth logN/(A — n) obtained 

 by subtracting the third from log N = 5*040107 7, which, 

 with practice, is easily done mentally as quickly as the 

 figures can be written down. The last is N 1 2 /(A— n) 1/2 . 

 Then the third is subtracted from the fifth and written 

 down on the right hand. This is logN 1 /2 /(A— nf 2 . Under 

 this is N 1/2 /(A — n) 3 < /2 , which, divided by 2 gives y m . 



The next step is to multiply the mantissse at the bottom of 

 the columns respectively by 2, 3, 4 and difference twice. 

 Similarly with the y. These operations are done beneath 

 as shown. The constants are then found at once. The 

 method also enables the values of Bf, ~dfi, "dot caused by 

 observation errors easily to be determined. 



Should it be desired to deal with another term film*, we 

 use four lines, multiply d m . y m by m 2 and difference three 

 times. Then 



f=S[5Q - V=A ! (»A«-?A ! (»«V.), 



a = A(m 2 dm) — f A(m 2 7 m ) — (2m + 1)^, 

 fi=m 2 d m — m 9 y m £—ma — m 2 /j,. 

 The University, Sheffield. 



LX XVIII. On the Dispersion of Carbon Dioxide in the 

 Infra-red Region of the Spectrum. By C. S'i'ATEbCU, 

 D.Sc, of the University of Bucharest*. 



ri>HEHE have been few investigations on the dispersion 

 JL of gases in the infra-red region of the spectrum. 



John Kochfj using an interference method, determined 

 the dispersion, for hydrogen, oxygen, air, carbon dioxide, 

 carbon monoxide, and methane, both in the visible spectrum 

 and in the infra-red. He found the latter by making use of 

 the " Keststrahlen " of calc-spar (X=6'7094/*) and of 

 gypsum (\ = S'61d± p). I myself u^ed a direct method, 

 that of minimum deviation, such as Biot and AragoJ used in 

 their determination of the refractive index of air. Mascart ^ 



* Communicated by Sir J. J. Thomson, O.M., F.R.S. 



T J. Koch, u Dispersionmess-UDgen an Gaseai im sichtboren und im 

 ultravoten Spectrum," Nova Acta Bey. Sue. Scient. Vpsaliensis, ser. 4, 

 vol. ii. Iso. 5. 



% .Biot. and Arajro, Memoires de la premiere classe de Vlnstitut. t. viii. 

 18(16. 



§ .Mascart, Annates de I'Ecole Norm. Sup. (2) vi. p. 1 (1877). 



