WHITE

, one of the colours of bodies. Though White cannot properly be said to be one colour, but rather a composition of all the colours together: for Newton has demonstrated that bodies only appear White by reflecting all the kinds of coloured rays alike; and that even the light of the sun is only White, because it consists of all colours mixed together.

This may be shewn mechanically in the following manner: Take seven parcels of coloured fine powders, the same as the primary colours of the rainbow, taking such quantities of these as shall be proportional to the respective breadths of these colours in the rainbow, which are of red 45 parts, orange 27, yellow 48, green 60, blue 60, indigo 40, and of violet 80; then mix intimately together these seven parcels of powders, and the mixture will be a pretty White colour: and this is only similar to the uniting the prismatic colours together again, to form a White ray or pencil of light of the whole of them. The same thing is done conveniently thus: Let the flat upper surface of a top be divided into 360 equal parts, all around its edge; then divide the same surface into seven sectors in the proportion of the numbers above, by seven radii or lines drawn from the centre; next let the respective colours be painted in a lively manner on these spaces, but so as the edge of each colour may be made nearly like the colour next adjoining, that the separation may not be well distinguished by the eye; then if the top be made to spin, the colours will thus seem to be mixed all together, and the whole surface will appear of a uniform whiteness: and if a large round black spot be painted in the middle, so as there may be only a broad flat ring of colours around it, the experiment will succeed the better. See Newton's Optics, prop. 6, book 1; and Ferguson's Tracts, pa. 296.

White bodies are found to take heat slower than black ones; because the latter absorb or imbibe rays of all kinds and colours, and the former reflect them. Hence it is that black paper is sooner put in flame, by a burning-glass, than White; and hence also black clothes, hung up in the sun by the dyers, dry sooner than white ones.