372 O. N. Rood on the Electric Spark. 
plate being ;%, of aninch. Another is represented in fig. » mag: 
nified 12 diameters ; the length of the ee was ;, of an inch. 
A large number of these markings were obtained on different 
plates, and their agreement in character is so decided that they 
cannot be attributed to accident os 
Further, their connexion can 
always be traced to certain nega- 
tive figures, and often into their 
interior. When two metallic 
points are used as before described, and positive and negative 
figures generated under them, it would be expected that these 
lines, marking passage e eeateninn: would extend from one 
figure to the other. This is not the case, the markings being 
le re; 
Se eat 
ge, over the sensitive surface, of cone a 
the minute and often r regular ications which attend sie de- 
velopment of the electric light under such circumstances. We 
should suppose that electricity would not produce much more 
than a streak more or Jess continuous under these circumstances, 
and these markings I consider among the most curious of the 
results obtained, suggesting as they “often do the perspective 
view of a cylinder wound with a right and left-handed spiral. 
No markings of this kind have in any case been observed in 
connexion with positive figures, and I have not obtained similar 
tracings by the use of frictional electricity. They are proms 
connected with the movable atmosphere, as they can often be 
sae directly to the impression left by this constituent of the 
Spar 
When the sensitive plate forms either the positive or negative 
electrode, and the length of the spark is ;'; of an inch, on re 
moving the plate into a dark room, it is fan d ee te develop- 
ment that a very small dark ring about 1_ of an inch in diam- 
eter has been produced. It is alwa : “nach fainter when the 
plate is used as 2 est sinscoies e iodid of silver be re- . 
moved from the film by hy aight of nk the eney 
positive and mo rings is considerably reduced, and 
then it becomes quite difficult to distinguish the positive figure. 
I cannot say at present whether these rings are produced by 
light, heat, or apes see: though the relative intensity of 
, and their occurrence on both electrodes, render the 
_ Supposition isitpscbialte 
| August Sist, 1864. 
