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36. Lichtenberg’s Experiment. Dust Figures. Pictures Drawn with Anode and Cathode. Göttingen, 1778-79. Motum Fluidi Electriciti.—He drew two independent superposed pictures upon a flat surface of an insulating material, for example, rosin. One picture was drawn with one terminal of a charged Leyden jar. Another picture was drawn with the other terminal of a charged Leyden jar. He sprinkled upon the surface over the two pictures, a dust made of a mixture of red lead and sulphur powder. The former became attracted to the picture drawn with the cathode, and the latter to that made with the anode, so that the two figures were clearly visible. Before sprinkling the powders upon the surface it is necessary to stir them together whereby they become oppositely electrified.

VIII

Arrangements for Taking Electrographs. ssss1, p. ssss1.

From Electrographs of Coins. ssss1, p. ssss1. Taken by Prof. McKay.

X

The sulphur arranges itself in tufts with diverging branches and the red lead in small circular patches. The particular materials, namely, the sulphur and red lead were first used by Villarsy. In case only one powder is employed, for example, licopodium, it adheres to both the positively and negatively electrified portion of the insulating plate, but in larger quantities upon the latter portions. Fig. X, shows rosin disc covered with licopodium powder after touching the disc with the knob of a Leyden jar.