Page:Collected Physical Papers.djvu/53

Rh with air and glass as dielectrics. The value for glass was found to be 2.7.

On the other hand, Lecher found that the dielectric constant rose with the frequency of vibration. Thus for plate glass—

There is thus a serious difference between the two views of the variation of K (and therefore of μ) with the frequency of vibration. In a previous paper, I alluded to the probability of the variation of μ with the frequency of vibration. The value of μ may at first undergo a diminution with the increase of frequency, reach a minimum, and then have the value augmented when the frequency rises above the critical rate. The result obtained by Lecher is, however, too divergent from the others to be explained by such a supposition.

The direct determination of μ for glass for electric oscillations of high frequency, seemed to me of interest, as throwing some light on the controversy. After the conclusion of my determination of the index for sulphur, I therefore commenced an investigation for the determination of μ for glass. This was, however, greatly delayed by repeated failures to cast glass locally and by my long absence from India. I then obtained from England two semi-cylinders of glass, with a radius = 12.5 cm. and height = 8 cm.

The method of experiment followed is the same as that described in my previous paper. The radiator