The Electric Spectrum of Liquid Water from Five to Twenty Centimeters

Abstract

A magnetron generator was used in the production of continuous electromagnetic radiation with wave-lengths ranging from five to twenty centimeters. The refractive index and absorption index of liquid water were determined for nineteen wave-lengths distributed over this region, by using two completely different methods of investigation. The conventional free wave method was studied and an expression for the energy transmitted through an absorption cell derived. This equation was experimentally verified but it is concluded that one must be very careful to exclude undesirable diffraction effects if satisfactory results are to be secured. It is also shown that several methods of calculation frequently applied are incorrect. A wire wave method suggested by the experiments of Seeberger is presented and discussed. This method is analyzed in detail and a simplified procedure is given in which the determinations of absorption index and refractive index are separated. The two methods were compared at a wave-length of 10.20 cm and an agreement between results to within one percent was secured. The wire wave method has a great advantage because of the high reproducibility of its results while the free wave method is laborious to use and its results are difficult to duplicate. The absorption index was observed to increase steadily from 0.048 at 20.44 cm to 0.153 at 4.80 cm. The average refractive index was 8.80 with only one point differing from the mean by more than 0.6 percent. Although there was no clear evidence of dispersion, reasons are given for expecting a slight variation of refractive index. The expected variation however lies within the limits of experimental error. A very complete comparison is given between the data presented in this paper and the abundant but discordant results previously published.