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138 The Daguerreotype and its Applications. 
small pictures. In one respect, these pictures are equal to those 
obtained with the achromatics; they are, however, inferior in oth- 
ers, and in their general effect. ‘The fine lines and edges of ob- 
jects are exceedingly sharp and distinct ; but the parts within the 
shade are not copied, and objects very distant frony that to which 
the focus was adjusted, are not — delineated. By placing 
a diaphragm before the lens, with aperture half an inch in 
diameter, the sharpness and distinctness of the lines and edges of 
objects are increased. In using this apparatus, which recommends 
itself by its cheapness—costing about twenty-five cents—the tube 
should be pushed in 3, or ;°; inch, after adjusting the lens to 
the luminous focus, to obtain that of the chemical rays. The 
exact distance the tube is to be retracted should be determined 
for each lens by trial. 
The folding doors of the French camera do not perfectly pro- 
tect the iodized plate, nor can they be always opened and closed 
with promptitude. ‘To obviate the inconveniences and risks 0¢- 
casioned by them, another contrivance, which dispenses with the 
use of doors, has been adopted for shielding the iodized surface 
from the action of light. The clean plate is placed and secured 
ina frame fitted to the back of the camera; this frame is grooved 
so as to allow a piece of tin to slide like the lid of a paint box in 
front of the silver surface. A narrow crevice is left in the camer@ 
when the tin is withdrawn, which may be closed by a piece of wood 
adapted to it, and attached by hinges to the side of the camera 
Another frame, similar to that just described, carries the ground 
glass. These frames should be so constructed that the ground 
glass and the plate shall occupy exactly the same position when 
one replaces the other. Instead of the deep iodine box which ac 
companies the French apparatus, one two inches deep, put much 
larger in every direction than the plate, is now commonly used. 
Iodization, however, can be effected with greater uniformity by 
placing the frame containing the plate on a board impregnated 
with iodine, than by any other arrangement. ‘The moistute 
which collects in the box, should be removed by sulphuric acid, 
a cup of which should remain in it. If this precaution 18 €3” 
lected, a film of water condenses on the plate, and is fatal to the ; 
success of the operation. » 
An inclination of 45° is ordinarily given to the plate when it 
is exposed to the vapor of mercury, to allow the proof to be ex 
amined as it comes out. A convenient mercurializing @pP* 
