16 Trans. Acad. Sci. of St. Louis. 



that the fogging effect was confined to a small area imme- 

 diately below the angle. This area was sharply defined. 



It was found very difficult to obtain any fogging effect 

 from the positive line. It required with the thicker covers 

 above the plates, from eight to ten thousand sparks when 

 the machine was working to its utmost limit, and the neg- 

 ative spark-gap was reduced to one cm. to obtain effects 

 which fifty sparks of the same length would produce in 

 the negative line. No discordant results were ever ob- 

 tained in the positive line. In the negative line many 

 were obtained. After a couple of years of almost daily 

 experimenting, it was found that fatigue or after effects 

 were produced in the hard rubber covers, which were of 

 sufficient influence to reverse the effects in short ex- 

 posures. An illustration of this after effect is shown in 

 Fig. C of Plate IX. It was found that the fogging effect 

 could be converged to a black focal line on the film, by 

 means of a small cylindrical fiber of red or white glass 

 laid upon the film below the angle and at right angles to 

 the wire. Such effects are shown in Fig. A of Plate IX. 

 The ends of such focal lines showed, after developing, 

 branching discharges, which proved conclusively that 

 electricity was escaping along the fiber in a lateral direc- 

 tion with respect to the discharge wire above. Such dis- 

 charges from the ends of a focal line are shown in Fig. B, 

 Plate IX, which is an enlarged copy of a portion of Fig. 

 A, where the glass fiber crosses the fogged area. When 

 such a glass fiber had been long and recently exposed, and 

 was then used on another plate, it gave a perfectly white 

 shadow picture, such as is shown in C of Plate IX. This 

 also indicates that the apparent refraction effects shown 

 in Figs. A and B are not due to ultra violet light or to 

 ether waves. 



Fig. A of Plate X shows shadow pictures of five red 

 glass fibers which had never been on the film of this plate, 

 but which had previously been exposed on another film in 

 the same holder. 



