This new science or art, has been distinguished by different names. It was first called _Photography_, from two Greek words, signifying _writing by light_: it was afterwards called the art of _Photogenic Drawing_, or drawing produced by light. M. Daguerre gave it the name of _Heliography_, or _writing by the sun_, all which appellatives are derived from the Greek, and are expressive, in some degree, of the nature of the process. We shall, however, make use of the term Daguerreotype, derived from the name of the inventor.
As it does not fall within our plan to give any minute descriptions of the Daguerreotype process, we shall just give a few general hints in reference to it, referring those who wish for particular details, to the separate treatises which have been published respecting it. The first thing necessary to be attended to in this art is, the preparation of the plate on which the drawing is to be made. The plate consists of a thin leaf of copper, plated with silver; both metals together, not being thicker than a card. The object of the copper is simply to support the silver, which must be the purest that can be procured. But though the copper should be no thicker than to serve the purpose of support, it is necessary that it should be so thick as to prevent the plate from being warped, which would produce a distortion of the images traced upon it. This plate must be polished;--and for this purpose, the following articles are required--a phial of olive oil--some very fine cotton--pumice-powder, ground till it is almost impalpable, and tied up in a piece of fine muslin, thin enough to let the powder pass through without touching the plate when the bag is shaken. A little nitric acid diluted with sixteen times, by measure, its own quantity of water--a frame of wire on which to place the plate, when being heated--a spirit lamp to make the plate hot--a small box with inclined sides within, and having a lid to shut it up close--and a square board large enough to hold the drawing, and having catches at the side to keep it steady.
To the above prerequisites, a good _Camera Obscura_ is, of course, essentially necessary. This instrument should be large enough to admit the plate of the largest drawing intended to be taken. The lens which forms the image of the object, should, if possible, be _achromatic_, and of a considerable diameter. In an excellent instrument of this description, now before me, the lens is an achromatic, about 3 inches diameter, but capable of being contracted to a smaller aperture. Its focal distance is about 17 inches; and the box, exclusive of the tube which contains the lens, is 15 inches long, 13-1/2 inches broad, and 11 inches deep. It forms a beautiful and well-defined picture of every well-enlightened object to which it is directed.