Dielectric Constant of Liquid Oxygen and Liquid Air. 365 



Professors Liveing and Dewar determined the refractive indices 

 (/*) corresponding to certain wave-lengths (X) for the following wave- 

 lengths : 



Prom lines in the 



spectrum of A. ^. 



Cadmium / 4416 corresponds to 1-2249 



" 16438 1-2211 



Thallium 5350 1*2219 



Lithium 6705 1-2210 



Sodium 5892 1*2114 



They state that they consider the best results are given by the first 

 two observations. Taking these wave-lengths 4416 and 6438, and 

 the refractive indices corresponding to them, we have calculated from 

 them, by the formula 



and found it to be 



x*-x? : 



the refractive index for infinite wave-length 

 as follows: 



/* = 1*2181. 



The square of this number is 1*4837, and this, therefore, is the value 

 of the square of the refractive index for waves of infinite wave-length 

 in liquid oxygen. 



Taking the product of the dielectric constant, K = 1*491, as above 

 determined, and that of the magnetic permeability, p 1*00287, as 

 previously obtained by us, we find that this product Kp is 1*495, and 

 hence that there is therefore a very fairly close agreement between 

 the number representing the square of the refractive index for waves 

 of infinite wave-length and the above product. The difference 

 amounts to about two-thirds of one per cent. Hence liquid oxygen 

 is a substance which very closely obeys Maxwell's law. 



We have applied the same apparatus to the determination of the 

 dielectric constant of liquid air obtained in exactly the same manner, 

 and Table II below gives the results of the observations taken in 

 liquid air. The observed results, when corrected as above described, 

 give for the dielectric constant of liquid air the number 1*495, which 

 is slightly more than that of the liquid oxygen. As, however, by the 

 time the experiment was complete the liquid air had practically 

 become liquid oxygen owing to the nearly complete evaporation of 

 ihe nitrogen, the coincidence of the two results is only what was to 

 be expected. 



Mag.,' October, 1893, " On the Refractive Indices of Liquid Nitrogen and Air;" 

 also Liveing and Dewar, 'Phil. Mag.,' Sept., 1888, " On the Absorption Spectrum 

 (luminous and ultra-violet) of large Masses of Oxygen." 



