138 The Daguerreotype and its AppUcatioris. 



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 from that to which 

 the focus was adjusted, are not accurately delineated. By placing 

 a diaphragm before the lens, with an 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 j-\ or j\ 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 oc- 

 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 

 in a 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 camera 

 when the tin is withdrawn, which may be closed by a piece of wood 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 apparatns, one two inches deep, but much 

 larger in every direction than the plate, is now commonly used, 

 lodization, 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 moisture 

 which collects in the box, should be removed by sulphuric acid, 

 a cup of which should remain in it. If this precaution is neg- 

 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 appara- 



