Page:Proceedings of the Royal Society of London Vol 60.djvu/392

Rh Professors Liveing and Dewar determined the refractive indices (fi) corresponding to certain wave-lengths for the following wavelengths :—

From lines in the spectrum of A. /a. „, . f 4416 corresponds to 12249 CadmlUm........... 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 .. _ M8—Mi /co X X* *

the refractive index for infinite wave-length (/<OT) and found it to be 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, = L00287, as previously obtained by ns, we find that this product Kp is 1-495, and hence that there is therefore a very fairly close agreement betweeu 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 the 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 A ir;” also Liveing and Dewar, ‘ Phil. Mag.,’ Sept., 1888, “ On the Absorption Spectrum (luminous and ultra-violet) of large Masses of Oxygen.”