TROWBRIDGE. — HIGH ELECTROMOTIVE FORI K. 1 
of branching at the positive and negative terminals, for this difference exhibited by 
the two poles of discharge is very marked. 
1'OWERFUL DISCHARGES OF ELECTRICITY AND V METHOD OF 
PHOTOGRAPHIC INTENSIFICATION OF THEIR IMA<iKS. 
The discharges from a large number of condensers, charged in multiple Mid die- 
charged in series, are probably more nearly identical with lightning discharges than 
any other forms of discharges within our experimental means ; and the photographs 
of such discharges reveal details which do not appear in the dischargee from Ruhmkorff 
coils or Tesla coils. 
With a large portrait lens many of such details appear which are not ihown b) 
small lenses. These details, however, are d tncult to reproduce. Indeed it often happens 
in scientific investigation that one obtains faint images which cannot be repro- 
duced by any process of printing, and which do not give satisfactory results with 
ordinary processes of intensification or methods of repeated printing from quick plates 
to slow plates. 
I have found the following method of obtaining trong contrasts in photography 
of electric sparks very useful in those cases where there is no general fog over the 
surface of the negative. 
The negative is first intensified by iodide of mercury. The formula is given in 
most books on photography, and is as follows: Dissolve 14 grs. of bichloride of mei 
cury in 700 c.c. of water and 42 grs. of iodide of potassium in 300 C.C of water; po 
odide solution into the mercury till the red precipitate formed is completely 
dissolved. For use, dilute with water and flow over the negative till the proper 
density is reached. When the negative is washed, it will turn yellow. I do not 
remove this yellow by hypo, for it is necessary to the complete success of the 
method of intensification. 
When the negative is dry, it is placed in full sunlight in the morning, when the 
beams of the sun are nearly horizontal. By suitably inclining the negative one can 
obt 
ided with a small stop, an image of the silver dep< sit 
which appears white on a yellow ground. The resulting photograph is therefor 
g 
The faintest silver deposit is reproduced in marked contrast to the back 
ground, which has reflected 
than that reflected from the 
y 
I believe that this process of intensification is valuable in the large number of 
es in which feeble imatt are obtained which do not lend themselves to the usual 
