156 SACHET, ON THE CAMERA LUCID A. 



for the purpose either of making varnish cells, or of mounting 

 preparations in fluid, that have been already fixed by hand. 

 A circular ring of brass, of sufficient diameter to hold a 

 watchmaker's or other lens, is also fitted to the under surface 

 of c, which may be raised or lowered by the milled head, as 

 required. Over this upon the upright (b) slides the apparatus 

 for direct heat (d), having two catches to fall on the point (/) 

 of c and retain it in either direction ; e is the turn-table 

 before alluded to, having the half and three-quarter circles 

 marked upon it, and also two stops (m n), in order that in case 

 of the removal of the slide before the mounting is complete, 

 it may be replaced without causing eccentricity. 



On the Camera Lucid a. By M. Nachet, Jun. 



In the last number of this journal, Mr. Gray has published 

 some suggestions on the subject of the Camera lucid a, which 

 lead me to suppose that the various descriptions hitherto 

 given of our camera, to be employed with the microscope in 

 the vertical position, have not been well understood by those 

 who have not seen the instrument. It will not therefore be 

 useless to offer some considerations, in order to show the 

 reasons which have induced us to adopt the arrangement in 

 question. All the forms of camera employed with the 

 microscope in the vertical* or inclined position may be 

 arranged in two classes j the first containing those forms in 

 which the camera gives the image of the object directly, and 

 that of the pencil by reflexion ; and the second, those, on the 

 other hand, in which the image of the object is given by 

 reflexion, and the pencil viewed directly. The best instance 

 of a camera belonging to the former category is that of 

 Amici, formed of a perforated steel mirror, and of a 

 prism jf the object being viewed through the opening, a, 

 of the mirror, and the pencil reflected by the prism being 

 seen on the annular surface, c, b. The inconveniences of 



* I may here remark that the vertical camera in itself (as a wliole) is not, 

 as Mr. Gray thinks, to be despised. Micrographers, who work in earnest, 

 often having to draw objects almost always immersed in fluid, and not 

 having to delay in order to remove a portion, as is done when objects are 

 prepared for preservation. 



f The arrangement of this camera has been altered by Chevalier, to 

 adapt it to the horizontal microscope. 



