Dictionarium polygraphicum. Blueness.

Dictionarium Polygraphicum:
Or, The Whole Body of Arts Regularly Digested.
Vol I.
London: Printed for C. Hitch and C. Davis in Pater-noster Row, and S. Austen in St. Paul's Church Yard. MDCCXXXV.
BLUENEss is the quality of any blue body; or it is such a size and texture of the parts, which composes the surface of a body, as disposes them to reflect the blue or azure rays of light, and those only to the eye.

As for the bluenes of the skies, sir Isaac Newton observes, that all the vapours, when they begin to condense and coalesce into natural particles, become first of such a bigness as to reflect the azure rays, before they can constitute clouds or any other colour.

This therefore being the first colour they begin to reflect, must be that of the finest and most transparent skies, in which the vapours are not arriv'd to a grossness sufficient to reflect other colours.

M. de la Hire, and before him Leonardo de Vinci observes, that any black body, view'd thro' a thin white one, gives the sensation of blue; and this he assigns as the reason of the blueness of the sky; the immense depth whereof being wholly devoid of light, is view'd thro’ the air, illuminated, and whitened by the sun.

For the same reason, he adds, it is, that soot, mixt with a white, makes a blue; for white bodies being always a little transparent, and mixing themselves with the black behind, give the perception of blue.

From the same principle, he accounts for the bluents of the veins on the surface of the skin, tho’ the blood they are fill’d with be a deep red; for he observes, that red, unless viewed in a strong clear light, appears a dark brown, bordering on black. Being then in a kind of obscurity, in the veins it must have the effect of a black; and this view'd through the membrane of the veins and the white skin, will produce the perception of blueness.

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