The distribution of electric force in the crookes dark space

Abstract

The electric force in the Crookes dark space and the negative glow has been the subject of a considerable number of investigations. The first determination was made by Schuster, whose results indicate the presence of a positive charge of electricity, whose density decreases in geometrical progression as the distance from the cathode increases in arithmetical progression. Graham found a curious drop in potential near the cathode, but Wehnalt, repeating these experiments, was unable to find this drop of potential, and ascribes it to the fact that the exploring points were not in the direct line of the current. Skinner§ came to the conclusion that all the fall of potential occurs at the surface of the cathode. Recently, Westphal|| has made a careful series of observations with cathodes of different metals in several gases, using a single exploring point, in which he finds a definite fall of potential— e. g . about 80 volts for Al in H 2 —at the surface of the cathode, the electric force a few millimetres away appearing from his curves nearly uniform. Now all these measurements were made by introducing exploring sounds, i. e . metallic wires or points, into the discharge, the observers trusting to these taking up the potential of the gas by which they were surrounded. The danger of such assumption has been pointed out by Sir J. J. Thomson, and for measurements made inside the dark space it seems entirely unwarranted.