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Page:Popular Science Monthly Volume 49.djvu/327

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311
PHOTOGRAPHING ELECTRICAL DISCHARGES.

lampblack driven off by the discharge, and the same peculiar formation is seen in the lightning flash as in Fig. 4. Between the dark filament of intact lampblack and the borders of the electric tracings there is a multitude of fine helicoidal curves filling the white traces left on the smoked glass. These helicoidal spires proceed to the right and left, and on about the middle of the trace the destruction of the two opposing motions produces the phenomena of discharge, viz., light, heat, sound, and mechanical effects. Zenger claims that these, his experiments, serve to show that the undulatory theory of Herz is very defective, there being no motion in plane waves, nor, as in the case of polarized light, is there any in circular or elliptical waves on a cylindrical surface.

"I could show," writes Prof. Zenger, in a recent letter to the writer, "that the solar phenomena, such as the solar corona and

PSM V49 D327 Imitation of the solar chromosphere and corona.jpg
Fig. 8.—Imitation of the Solar Chromosphere and Corona.

protuberances, are also due to electric discharges continually given off from the sun's surface. Fig. 7 shows the effect of positive discharges from a circular disk of tin foil into the smoked surface of a glass plate. It will be noticed that we have facsimiles of all the forms of solar protuberances. In Fig. 8 we see the effect of a positive discharge from a hollow hemisphere into the smoked surface of a glass plate, on the middle of which was fixed a lump of wax. The effects are analogous to the chromosphere and to the inner and outer layers of the solar corona produced by the superposition of the lines of electric force radiating from different parts of the spherical surface."

Prof. Zenger's photographs are remarkably interesting and