The power of making such a representation of any object, as shall give a distinct idea of its form, is a faculty which artists possess in different degrees of perfection. The principal difficulty is, to get a first delineation of any subject; from this a copy may be made in various ways, with less exertion of talent than was required for the composition of the original.

Various geometrical and optical inventions have been proposed to assist the artist in making an outline of an object which he wishes to represent. The Reticulated Square and other contrivances, for placing every point of the thing to be represented in its proper place in the picture, belong to the first class; the Camera Obscura and the Camera Lucida to the second. When a design is to be copied, a different kind of contrivances will in general be more convenient. It is only of these that I propose to treat here.