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means, which could scarcely ever be thought of by a per-son conversant in that art singly, but which a generalknowledge of the others may be expected to suggest.

SECT. I.

General observations on black colours.

O F black, as of other colours, there are many shades orvarieties; different bodies, truly and simply black, orwhich have no sensible admixture of any of the rest of thecolours, as black velvet, fine black cloth, the feathers ofthe raven, &c. appearing, when placed together, of teintsvery sensibly different.

2. One and the same body also assumes different degreesof blackness, according to the disposition of the sensibleparts of its surface; and in this respect, there is not, per-haps, any other colour, which is so much affected by anapparent mechanism. Thus black velvet, when the pileis raised, appears intensely black, much more so than thesilk it was made from; but on pressing the pile smooth,it looks pale, and, in certain positions, shews somewhateven of a whitish cast.

3. This observation is agreeable to the physical theory,which ascribes the blackness of bodies to the luminous rays,that fall upon them, being in great part absorbed, or stifledin their pores. When the surface is composed of a multi-tude of loose filaments, or small points, with the extremi-ties turned towards the eye, much of the light is stifled inthe interstices between them, and the body appears dark:when the filaments are pressed close, or the surface smooth-ed and polished, more of the light is reflected from it, andthe intensity of the blackness is diminished; thoughthe beauty may be improved by the glossiness which reftiltsfrom the smoothing.

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