Newton having produced seven colours from a beam of light analytically, by prismatic refraction, and hat unable to resolve either of them into other colours by prat; them alternately through a second prism, concluded that the were seven primary colours.

Nevertheless, three of these, blue, red, and yellow, being separated from the others and properly compounded, reproduce colourless light, which again, by prismatic refraction, afford Newton's seven primaries, including green, orange, violet and indigo; and so on repeatedly.

Another difficulty into which Newton's hvpothesis led,on the necessity of admitting two kinds of colours, which tit de-nominated homogeneal and heterogeneal; thus his prisesive green was homogeneal, but a green composed of blue and yellow he culled heterogeneal; yet, had he mixed his blue and yellow rays, his prism would have refracted without separating than. and thus the heterogeueal colour would have become homo-geneal; we shall not, however, continue an argument which will make artists smile and grave men frown; yet, neither false shame, nor respect for authority, however exalted, ought a any case, to suppress our regard for and vindication of truth In the present case, too, that great roan, Newton himself, admonishes us not to admit more causes of natural appearances than are both true and sufficient to explain then, agreeably by that more antient maxim, that nature does nothing in rata. and. therefore, would not have instituted seven primaries in a design which is perfectly accompli shed by three. But philosophies ore rediscovering the facts, and taking gradually the pestisites of the artist upon which the true relations and science of colours depend.