Page:Proceedings of the Royal Society of London Vol 60.djvu/391

364 as the dielectric constant or Liquid oxygen referred to that of the overlying gaseous oxygen at —182° C. as unity. Since the aluminium condenser is at the same temperature when the two measurements 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 0° C. and 760 mm. is 1-00059. That of oxygen gas at the same temperature and pressure is not very different. If the value of K —1 for gases varies directly as the pressure, and if temperature perse 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 lo 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° 0. 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 constant and the magnetic permeability should be equal to the square of the refractive index for waves of infinite wave-length ? 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

“ On the M agnetic Perm eability of L iquid Oxygen and Liquid A ir.” f Liveing and Dewar, ‘Phil. Mag.,’ Sept., 1895, p. 269, “ On tlie Refraction and Dispersion of L iquid Oxygen and the Absorption Spectrum of Liquid Air. See also Liveing and Dewar “ On the Refractive Index of Liquid Oxygen, ‘ Phil. Mag.,’ A ugust, 1892, “ On the Spectrum of Liquid Oxygen and on the Refractive Indices of Liquid N itrous Oxide and E thylene;” also Liveing and Dewar, ‘ Phil.
 * gee Flem ing and Dewar, ‘ Roy. Soc. Proc.,’ December, 1896, vol. 60, p. 283,