The works of the Honourable Robert Boyle, Esq., epitomiz'd by Richard Boulton ... ; illustrated with copper plates.

EXPERIMENT XVII.

HAving mix'd Colour'd Powders together, I observ'd, that if a Liquor was made use of in the Mixture, the same Colour would not emerge as from the dry Powders. Orpiment and Yellow Oker being mix'd afford a good Green. A Yellow solution of Gold in Aqua fortis being mix'd with a blew Solution of crude Copper by shaking yielded a transparent Green: And so did blew and yellow Amel melted together: Whether this compound Colour proceeds from a Union of Rays, or else from the joint Effect they have upon the Retina, as when two Strings sound at the same time they make one united Sound I shall not now stay to Examine; but shall briefly intimate that by a good Microscope I

could discern each of the Powders of the Bise and Orpiment Distinct, so that a Transposition and Juxtaposition of Parts may produce a new Colour, by variously modifying and reflect∣ing the Rays of Light that fall upon them. So that Colours being mechanically produc'd, there is no need of substantial Forms to explicate them; nor do they seem to be such inherent Colours as they would have them to be, since they consist only of a heap of mix'd Particles of Matter. Nor does it appear, how these compound Co∣lours should be caus'd by a Sulphur, which tho' the Ingredients must contain it, cause no such Effect there.