Short Electric Waves.

E. F. Nichals and J. D. Tear. Short Electric Waves. Journ. of Francl. Inst., V. 194, No. 5, p. 683, Nov. 1922 (Abstract).

The authors of the present work have apparently succeeded, insofar as the cited preliminary communication permits one to judge, in taking a major step forward in the question of obtaining short electric waves.

The vibrator is a modified form of Tear’s dipole, with certain additions that make it possible to obtain shorter waves. The spark discharge takes place between the bases of two tungsten cylinders immersed in kerosene. The cylinders were soldered to the ends of thin glass tubes of refractory glass and were set by means of a micrometer, which made it possible to regulate the spark gap between them; the smallest cylinders used had a diameter of 0.2 mm and a height of 0.2 mm. The high-voltage wires were brought inside the glass tubes to within a distance of several millimeters of the tungsten cylinders; the spark jumped to the cylinders across an air gap, which was continuously blown with compressed air for the purpose of deionizing and cooling the place where the glass was soldered to the tungsten. With a cylinder spacing of about 0.01 mm, each discharge produces

electric oscillations in a dipole, strongly damped, whose wavelength, as experiments have shown, is 3–5 times greater than the length of the dipole (the factor 5 applies to small dipoles).

The vibrator was placed on an optical bench at the principal focus of a paraffin lens; then the waves passed as a bundle of parallel rays through an interference apparatus or another optical system, and were collected by a second lens on the receiving apparatus.

As the receiving apparatus Nichols’s radiometer was used, which made it possible to obtain much greater sensitivity than with the earlier methods (a thermoelement with a galvanometer, a thermogalvanometer); the total weight of the moving system of the radiometer was about 0.5 mgr. The receiving elements consisted either of platinum wire of diameter \(1\mu\) and of appropriate length, in order to obtain resonance with the received radiation, or of a metallic film deposited on sheets of mica or quartz thread by evaporation in vacuum; these receiving elements were placed in place of the usual blackened vanes of the radiometer. Thin mica shields, placed at a distance of about 0.1 mm in front of or behind the receiving element, made the radiometric effect of both vanes one-sided.

The wavelength was measured with a Boltzmann mirror interferometer, and also with a reflecting echelon consisting of precisely calibrated brass plates. The echelon was also used for an approximate analysis of the dipole radiation and for isolating a more homogeneous radiation of the desired wavelength.

By the method described, electric waves from several centimeters down to 1.8 mm in length were isolated. Under favorable conditions, a wavelength of 0.8 mm was also accessible to observation.

Thus the electric spectrum can evidently be studied more completely than has been possible up to now¹, by another two or three octaves toward shorter waves.

S. Rzhevkin.

1. See, for example, the review of Mebius’s work, Uspekhi Fizicheskikh Nauk, Vol. III, issue 1, p. 121. ↩