Theory of Refraction in Gases. 4()5 



the facts tbey are only partial representations of the ^vhok^ 

 facts, and quite at variance with some features of the 

 phenomena. 



(1) Sftmmary of Experimental Evidence. 



Before proceedino- to discuss these theories and to frame a 

 new theory, it is desirable to summarize as briefly as possible 

 the experimental facts in our possession. 



First. — The Dielectric Constant of Gases. 



Boltzmaun^ and Klemencicf made measurements of the 

 value of K for several gases at ordinary temperatures. They 

 found that K — I was very nearly proportional to the pressure. 

 They did not, however^ measure the effect of temperature. 



Baedecker X has measured the effect of temperature on the 

 value of K for some of the denser gases in which (K — 1) is 

 much greater than (yu,^ — 1) ; and I have shown § that his 

 results for sulphur dioxide and ammonia agree extremely well 



p 

 with the law K — Ix — , P being the pressure and 6 the 



absolute temperature. 



Second. — The Refractive Index of Gases. 



Perhaps the most extensive measurements up to the present 

 time have been made by Mascart ||, Ketteler^, and Lorenz ^^. 

 Their results show that /-t^ — 1 is very nearly proportional to the 

 pressure. 



Mascart is the only observer who measured the effect of 

 temperature for a number of gases- He found that the effect 

 of temperature was greater than that indicated by the 



p 



theoretical law u^ — 1 cc ^ 



u ' 



Recently the present writer ft measured with great care 

 the temperature effect on refraction in several gases, the 

 range of temperature being much greater than that used by 

 Mascart. The values obtained were in every case less than 

 those obtained by Mascart, but they still show a divergence 



p 

 from the law yit^ — Ix^. In the case of hydrogen /z^ — 1 



diminished less with increasing temperature than the theo- 

 retical law indicates. 



* Annalen der Physik, civ. p. 403 (1875). 



t Wien. Berichte, xci. p. 712 (1885). 



X Zeitschrift Phys. Chem. vol. xxxvi. p. 305. § L. c. ante. 



II Annahs de Vecole normale, vi. p. 9 (1877). 



^ Annalen der Physik (Pogg.), cxxiv. (1865). 

 ** Annalen der Physik, xi. (1880). 

 tt Phil. Trans, cci. p. 435 (1903). 



Phil. Mag. S. 6. Vol. 6. No. .34. Oct. 1903. 2 H 



