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 ecm. 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. 
