The Dielectric Properties of Water for Continuous Waves

Direct measurement of the refractive index of water for continuous waves of length about 2 meters.—In the method adopted continuous standing waves on wires were measured both in air and in water, and the refractive index determined as the ratio. Errors involved in the measurement of the length of waves in air due to imperfect reflection and to the resistance of the guiding wires, were investigated. In the case of water it was found that measurements varied with the size of the tank unless the waves were guided into the water by conductors extending through the tank. The final arrangement is analogous to Kundt's tube for sound waves; the level of the water in a vertical tube through which the parallel wires passed, was varied and the nodes determined from the variation of the current from a thermocouple placed in the bridge of the Lecher system, located at the lower end of the water column. Thus a number of nodes were located. The mean result for the refractive index comes out 8.88±.04, in good agreement with values obtained by others using discontinuous waves. This indicates that within the range of frequencies investigated, the group velocity of waves through water is the same as their phase velocity, within the accuracy of the measurements. No appreciable dispersion for the range of wave-lengths 124 and 276 cm was observed.

An oscillating circuit for producing short continuous Hertzian waves of length varying from 1 meter up, is described, in which the tube capacity is used as a means of coupling.