Electric Lnghts for Photo-micrography. 297 
trays of ten elements, at five pounds sterling per tray, and I find 
that a battery of five trays is sufficient for most a Seven 
pounds and a half of strong commercial nitric acid, and three of 
sulphuric, diluted with ten times the quantity of water, is suffi- 
cient to charge this battery, which will then produce the light 
continuously for from three to four hours. The cost of running 
the battery for this time, including in the estimate the amount 
of zinc consumed, and the cost of amalgamating every third or 
fourth time of using, is very moderate. I make it a practice to 
have the battery washed out, the acids thrown away and the 
porous cups put to soak immediately after I have done the day’s 
work, and all this is so simple that I have no difficulty in in- 
structing an orderly to do it, so that the management of the bat- 
tery does not occupy any part of my time. 
The Duboscq’s lamp, the microscope and the plate holder are 
arranged in a dark room which enables me to dispense with the 
use of a camera. The general arrangement of the apparatus is 
shown in the cut. 
The electric lamp of Dubosegq (a) is placed on a stool against 
the wall at one ma of the room, and its light concentrated by a 
pair of condensing lenses (2) on the lower lens of the achromatic 
condenser of the microscope. The microscope (c) (a large Powell 
and Lealand’s stand) is placed on a small table (e) which is so 
arranged that it can be lowered or elevated at pleasure and can 
be levelled by means of three levelling screws at its base. 
The plate holder (g), also arranged so that it can be raised or 
lowered at pleasure, is supported by a small table (7) which 
Stands on three levelling screws. _The floor of the apartment is 
quite level. The lenses employed for the microscope are 1 
of Mr. William Wales of Fort Lee, New Jersey,. specially 
lowered and moved from nde to side till the center of the achro- 
fixed just below the achromatic condenser, and not only 
Vents the admission of non-actinic rays, but excludes the td 
ieee: ghee 
8teat heat which accompanies the electric light, an 
