808 



Dr. G. Rudorf on the Molecular and 



Part III. — Calculation of the Refractive Indices 

 of the Liquefied Gases. 



The formula proposed by Lorentz and Lorenz for the 

 relation between the refractive index and the density is 

 supposed to be independent of the state of aggregation. 

 Indeed, this generally seems to be the case. Knowing then 

 the refractive index of the gas and the densities of the gas 

 and liquid, we can calculate the refractive index of the liquid. 

 The table gives the results of the calculations. 





^gas- 



Pgas- 



)U 2 -1 1 



^liquid' 



^liquid- 



He 



1-0000347 



0-0001769 



0131 



0-15 



103 



Ne 



1-0000685 



000089 



0-051 



? 



? 



A 



1-0002792 



0-001782 



0104 



1-423 



1-23 



Xr 



1-0004189 



0-003709 



0-075 



2-155 



1-26 



X 



1-0006823 



0-00584 



0-078 



3-52 



1-46 





Whether these figures will prove to be correct or not 

 remains to be seen. As we have taken the values of /j, for 

 X = oo , the values of /^liquid are also for \=co . But as the 

 dispersion formulae are known, //, can be calculated for any 

 value of X. Nothing is yet known about the refractive 

 indices or dispersion of these gases in the liquid state, except 

 that the refractive index of helium is certainly very low. It 

 ought not to be difficult to determine /ju for liquid argon, as 

 plenty of this substance is now easily procurable. 



Part IV. — Note on Lord Kelvin's paper on the 

 Sizes of Atoms (Phil. Mag. [H] iv. p. 177 (1902)). 



After the foregoing calculations were completed I found 

 in W. P. Boynton's ' Kinetic Theory/ p. 278, a reference to 

 a paper by Lord Kelvin, in which he had calculated the mean 

 free path and molecular diameter of several' gases, includino- 

 argon. The result obtained by him for the value of L : 

 3'89 X 10 — 6 cm. was so different from my own : 

 10'07 x 10 -6 cm., although he had used practically the same 

 experimental data, that I felt compelled to look for the cause 

 of this discrepancy. 



