366 O. N. Rood on the Electric Spark. 
Length of discharge 2; inch. The forms are as above de- 
scribed. 
tric 
ure like 1, (in the first No. of this memoir), 
except that the central portion of the disc is 
occupied by a dark disc; others resemble the figure marked .5 
in the same wood-cut, except that the two fine rings are not re- 
produced in the induction figure. 
1,'5 inches, more or less irregular star, as seen in fig. 7, 
resembling in many respects those pro- 
duced by frictional electricity ; the fine 
rings however being absent. It seems 
to consist of two parts, a star with a 
sharp outline, and a circular mass of 
shade, which, when unsymmetrically 
placed, is seen to be distinct from the 
star as in fig. 8. The starlike portion corresponds with that 
shown in fig. 4, and the black dise with the black ring there 
figured. 
8. 
this memoir; it is to be remarked, however, that the lines 
making up the figure are much thicker, viewed under the micro- 
scope, as if they had been traced by a blunt quill instead of a 
fine steel pen. 
