364 Profs. J. A. Fleming and J. Dewar. On the 



as the dielectric constant of liquid oxygen referred to that of the 

 overlying gaseous oxygen at 182 C. as unity. Since the alumi- 

 nium condenser is at the same temperature when the two measure- 

 ments are made, no correction is necessary for any change of form 

 of the condenser. 



To determine the dielectric constant of liquid oxygen in terms of 

 that of a vacuum taken as unity, we require to know the dielectric 

 constant of the gaseous oxygen lying on the surface of the liquid 

 oxygen referred to the same unit. 



Boltzmann and Klemencic have both shown that the true dielectric 

 constant of air at a temperature of C. and 760 mm. is 1*00059. 

 That of oxygen gas at the same temperature and pressure is not 

 very different. Tf the value of K 1 for gases varies directly as 

 the pressure, and if temperature per se makes no difference, then the 

 dielectric constant of the gaseous oxygen lying on the surface of the 

 liquid oxygen, and which has a temperature of 182 C. nearly, and 

 a . density about three times that of the gas at 15 C., is not far 

 from 1*002. Hence the correcting factor to be applied to the above 

 value of the dielectric constant of the liquid is at the most 1*002, 

 and the true dielectric constant of liquid oxygen at 182 C. and 

 under a pressure of 760 mm. is not far from 1*493. 



We intend to examine this correction more closely. 



As a matter of fact, we were not able to detect any difference 

 between the capacity of the small condenser when held in air at 

 ordinary temperature (15 C.) and pressure, and in the cold gaseous 

 oxygen at 182 C. lying on the surface of the liquid oxygen. 



Until we are able to make a better determination we may take the 

 above number, . 1 '491, therefore, as representing in all probability a 

 close approximation to the dielectric constant of liquid oxygen. 



The interesting question then arises how far does liquid oxygen 

 obey Maxwell's law, by which the product of the dielectric con- 

 stant and the magnetic permeability should be equal to the 

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

 The materials are at hand for making this comparison, as we have 

 ourselves just determined the magnetic permeability of liquid 

 oxygen, and find it to be 1*00287,* and the refractive index of liquid 

 oxygen has been determined by Professors Liveing and Dewar for 

 several different wave-lengths.f 



* See Fleming and Dewar, ' Eoy. Soc. Proc.,' December, 1896, vol. 60, p. 283, 

 "On the Magnetic Permeability of Liquid Oxygen and Liquid Air." 



t Liveing and Dewar, ' Phil. Mag.,' Sept., 1895, p. 269, " On the Eefraction 

 and Dispersion of Liquid Oxygen and the Absorption Spectrum of Liquid Air." 

 See also Liveing and Dewar " On the Refractive Index of Liquid Oxygen," ' Phil. 

 Mag.,' August, 1892, " On the Spectrum of Liquid Oxygen and on the Kefractive 

 Indices of Liquid Nitrous Oxide and Etliylene;" also Liveing and Dewar, 'Phil. 



