160 O. N. Rood on the discharge of a Leyden jar. 
a burning splinter of wood. 
The duration was found to vary from 
000003 
"000007 
of a second. The rate of rotation was 206 per second. De- 
terminations of this same point had previously been made at 
an early stage of the work ; their result was 
*000008 
000006 
of a second. There can be no doubt but that the duration of 
the yellow portion in individual sparks varies within limits like 
the above as can be seen by a comparison of successive dis- 
charges. 
use of the micrometer. This proves of course that the first 
discharge is a simple act, and isolated from those that follow. 
Next, as an appropriate termination to this experiment, I 
blackened, all the surface of the strip of white paper except 80 
much as served to form a square. On examining the image 0 
this with the same rate of rotation, the square was tolerably 
