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of imbibition which we often find possessed in the same sheet, owing to trifling inequalities in its texture. This is, to a certain extent, to be overcome by a careful examination of each sheet, by the light of a candle or lamp at night, or in the dark. By extending each sheet between the light and the eye, and slowly moving it up and down, and from left to right, the variations in its texture will be seen by the different quantities of light which pass through it in different parts; and it is always the safest course to reject every sheet in which inequalities exist. Paper sometimes contains minute portions of thread, black or brown specks, and other imperfections, all of which materially interfere with the process. Some paper has an artificial substance given to it by sulphate of lime (Plaster of Paris); this defect only exists, however, in the cheaper sorts of demy, and therefore can be easily avoided. In all cases such paper should be rejected, as no really sensitive material can be obtained with it. Paper-makers, as is well known, often affix their name to one half the sheet; this moiety should also be placed aside, as the letters must frequently come out with annoying distinctness. Well sized paper is by no means objectionable, indeed, is rather to be preferred, since the size tends to exalt the sensitive powers of the silver. The principal thing to be avoided, is the absorption of the sensitive solution into the pores; and it must be evident that this desideratum cannot be obtained by unsized paper. Taking all things into consideration, the paper known as satin post would appear to be preferable,