The spectres may be easily made to appear life-sized or colossal, by having the plate _nearer_ the eyes while receiving the impression, and by _increasing the distance_ between the observer and the surface against which they are seen. As a general rule, the observer should be about eight to twenty feet from the surface. When the spectres are seen against opposite houses, the sky, and other distant surfaces, they will appear colossal. Should any one not be able to see the spectre’s features, the reason will be, either that the eyes have been allowed to wander, or the head to move, while looking at the plate. Many persons will see some one coloured spectre better than the others, in consequence of their eyes not being equally sensitive to all colours. The colours in the plate will be found to reverse themselves in the spectres, as explained elsewhere, the spectres always appearing of the complementary colour to that of the plate from which it is obtained. Thus, blue will appear orange, and orange blue, &c. LIST OF THE PLATES. PLATE I. This winged figure of Victory will give a white spectre by artificial light (rather green by daylight), the red wreaths green, the green roses red, and the orange stars blue. PLATE II. This black figure will give a white spectre. PLATE III. This will give a dark spectre. PLATE IV. This green figure will give a red spectre. PLATE V. And this red figure will give a green spectre. PLATE VI. This orange figure will give a blue spectre. PLATE VII. And this blue figure an orange spectre. PLATE VIII. This purple hand will give a yellow spectre. PLATE IX. And this yellow figure of Victory will give a purple spectre. PLATE X. The face of this figure will come out green in the spectre, the garment red, and the cloud white. PLATE XI. This black skeleton will make a white spectre. PLATE XII. This skeleton will also give a white spectre, with a yellow mantle. PLATE XIII. This figure and broom will give a yellow spectre, cloak and hat red, and moon white. PLATE XIV. These figures will give green and yellow spectres. PLATE XV. This Cupid will give a rose-coloured spectre, with bow and arrow yellow. PLATE XVI. This is a rainbow with colours reversed, the spectre of which will be found a good resemblance of nature, especially when seen on a cloudy sky. * * * * * The colours of the spectres produced by these figures will not only be subject to a slight variation in different eyes, but also by the degree in which the plates are illuminated while being looked at. A POPULAR AND SCIENTIFIC DESCRIPTION.