I 



PHOTOGRAPHING ELECTRICAL DISCHARGES. 311 



ampblack driven off by the discharge, and the same peculiar for- 

 ation 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 

 hite traces left on the smoked glass. These helicoidal spires 

 roceed to the right and left, and on about the middle of the trace 

 he destruction of the two opposing motions produces the phe- 

 omena of discharge, viz., light, heat, sound, and mechanical 

 ffects. Zenger claims that these, his experiments, serve to show 

 hat the undulatory theory of Herz is very defective, there 

 eing no motion in plane waves, nor, as in the case of polarized 

 ight, is there any in circular or elliptical waves on a cylindrical 

 urface. 



" I could show," writes Prof. Zenger, in a recent letter to the 

 riter, " that the solar phenomena, such as the solar corona and 



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 posi- 

 tive discharges from a circular disk of tin foil into the smoked 

 surface of a glass plate. It will be noticed that we have facsimi- 

 les 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 



