Chap. 2. PHILOSOPHY.

3.5X

moifture, and perhaps augmented likewife by the accretion*of the earthy and oily parts of that moiflure. How the men-tioned colours fhould arife from increaling the bulk of tholeparticles, is evident; feeing thole colours lie without the ring ofgreen between the glalTes, and are therefore formed wherethe tranfparent fubftance which reflects them is thicker-And that the augmentation of the denlity of the colorificparticles will' confpire to the production of the fame effect,.will be evident; if we remember what was faid of the dif-ferent fize of the rings, when air was included between theglaftes, from their fize when water was between them ;which fhewed that a fubftance of a greater denfity than*another gives the fame colour at a lefs thicknefs. Now'the changes likely to be wrought in the denfity or magni-tude of the parts of vegetables by withering feem notgreater, than are fufficient to change their colour into thofe ofthe lame order; but the yellow and red of the fourthorder.are not full enough to agree with thofe, into which thefe fub-ftances change, nor is the green of the fecond fufficientlygood to be the colour of vegetables ; lo that their colourmu ft of necefiity be of the third order.

X y. The blue colour of fyrup of violets our author*fuppofes to be of the third order; for acids, as vinegar, with,this fyrup change it red, and fait of tartar or other alca-lies mixed therewith turn it green. But if the blue colour -of the fyrup were of the fecond order, the red colour,,which acids by attenuating its parts give it, mull be of the •firft order, and the green given it by alcalies by incraflating;