294 J. J. Woodward on the Magnesium and 
excited surface.* This seems proved beyond doubt by the iden- 
tity of the Lichtenberg figures, with the depression figures pro- 
duced on developing. No chemical change of the pitch could 
enable it to attract dust. : 
As the point of temperature at which developement begins 
is considerably below the true fusing point of the pitch, the 
erformed by the electricity is no inconsiderable quantity. 
Does the electricity disappear in performing this work? The 
fact that the depression of the surface stops at a certain pomt, 
while the attraction for the opposite E on the metal plate should 
be constantly growing stronger, seems to point to an affirmative 
answer. As pitch, however, is said to become a conductor when 
fused, it may be that the two electricities are gradually trans- 
mitted and neutralize each other. Experiments have been un- 
dertaken in the hope of obtaining a decisive answer to this 
question, but as yet with no result worthy of publication. 
Cornell Univ., Ithaca, N, Y., Feb. 6th, 1870, 
Army, dated Army Medical Museum, Microscopical Section, 
January 4, 1870.+ 
es of the treasures of the Museum. In these experiments 
used the sun as a source of illumination, and, following the 
which I have described in ful ; f 
ulty in arranging a method, by the aid of which this class © 
objects could be photographed quite as successfully and readily 
as the diatoms and other test objects which had previously we 
so satisfactorily reproduced in this section of the Museum. 
shall take occasion in the course of a few days to lay before yo" 
_* The laws of attraction and repulsio itive and negative is 
___ ity being the same, itis mot clear wo whit cares the iference of the figures # 
_ {Communicated for this Journal by Lieut. Col. J. J. Woodward. 
_ | fCireular No. 6, War Dep: ent, Surgeon General’s Office, Nov. 1, 1865, pase 
et. seg. 5 this Jo i, vol. xlii, Sept., 1866. 
1 elsewhere,t I had no dif- 
‘i 
* 
ie a 
