O. N. Rood on the discharge of a Leyden jar. 157 
will be thrown on the ground glass only when the mirror hap- 
pens to be in a favorable position, still as several of them oc- 
curred in a second, and as the mirror was always double it did 
a fraction of a second before it discharges itself backward 
through the coil. . 
Appearance presented by the spark, viewed with the stationary 
mirror. 
., (a) With brass bails as electrodes. Here the spark presented 
its ordinary well known appearance, being merely magnified by 
the eye-piece. Bs 
(6) With pointed wires as electrodes, When the “striking 
: distance” was one millimeter, 
the form was that represented 
in figure 2 at A, viz: a cen- 
rtion surrounded 
The green color 
shown farther on, 
