270 Profs. Liveing and Dewar on the Refraction 

 constant by Gladstone's formula becomes-^- =0*1953, and 



U? —~ 1 



by Lorenz's formula, , 2 ■ ow == , 1242. 



Taking Regnault's value for the density of oxygen gas at 

 0° and 76 centim., viz. 000143, and Mascart's value for the 

 mean refractive index, viz. 1*000271, we find for gaseous 

 oxygen the refraction-constant 





d 

 and V? — 1 



1 =0-18947 

 = 0-12631. 



(fJL 2 + 2)d 



It will be seen that this last is nearly equal to the refraction- 

 constant as above determined for the liquid. 



In Mascart's paper " Sur la Refraction des Gaz " {Annates 

 L'JEcole Normale Expdrimentale, 1876) some observations 

 on the Dispersion of Oxygen and other Gases were given, 

 which enable a comparison to be made between this property 

 in the gaseous and liquid states. Taking Cauchy's formula 



n 



-l = a(l4 2 ) 



then 1^ _ 1_ 



n' — n , A/ 2 X s 



n+l : ., , b 

 X 



l+h 



From this b is calculated by Mascart, and is called the Co- 

 efficient of Dispersion. The blue and red cadmium lines 

 represent the extremest difference of wave-lengths employed. 

 This gave for oxygen the maximum and minimum values 

 0*0049 and 00078, and a mean value 0'0064for the Constant 

 of Dispersion. Taking the values for the liquid state given 

 above, the value of b becomes 0'0064. It seems possible, 

 therefore, that the Dispersion Constant in the liquid state is 

 identical with that of the gas. 



In a recent conversation with M. Cornu about the absorp- 

 tion-spectrum of liquid oxygen, he suggested that it would be 

 interesting to ascertain whether the diffuse absorption-bands 

 were equally well developed when the increased density of 

 the oxygen was produced by reduction of temperature at 

 atmospheric pressure as when the gas was compressed at 

 higher temperatures. 



M. Janssen has found that the intensity of these diffuse 



