BLACKNESS

, the quality of a black body, as to colour; arising from its stifling or absorbing the rays of light, and reflecting little or none. In which sense it stands directly opposed to whiteness; which consists in such a texture of parts, as indifferently reflects all the rays thrown upon it, of whatever colour they may be,

Descartes, it seems, first rightly distinguished these causes of black and white, though he might be mistaken with respect to the general nature of light and colours. —Sir lsaac Newton shews, in his Optics, that to produce black colours, the corpuscles must be smaller than for exhibiting the other colours; because, where the sizes of the component particles of a body are greater, the light reflected is too much for constituting this colour: but when they are a little smaller than is requisite to reflect the white, and very faint blue of the first order, they will reflect so little light, as to appear intensely black; and yet they may perhaps reflect it variously to and fro within them so long, till it be stifled and lost.

And hence, it appears, why fire, or putrefaction, by dividing the particles of substances, turn them black: why small quantities of black substances impart their colours very freely, and intensely, to other substances, to which they are applied; the minute particles of these, on account of their very great number, easily overspreading the gross particles of others. Hence it also appears, why glass ground very elaborately on a copper-plate with sand, till it be well polished, makes the sand, with what is rubbed off from the copper and glass, become very black: also why blacks commonly incline a little towards a blueish colour; as may be seen by illuminating white paper with light reflected from black substances, when the paper usually appears of a blueish white; the reason of which is, that black borders on the obscure blue of the first order of colours, and therefore reflects more rays of that colour than of any other: and lastly why black substances do sooner than others become hot in the sun's light, and burn; an effect which may proceed partly from the multitude of refractions in a little space, and partly from the easy commotion among such minute particles.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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BIQUADRATE
BIQUINTILE
BISECTION
BISSEXTILE
BLACK
* BLACKNESS
BLAGRAVE (John)
BLAIR (John)
BLIND
BLINDNESS
BLINDS