A NEW THEORY OF LIGHT AND COLOURS. 47 l 



fractions. But if trial shall be made with colours not thoroughly- 

 separated, there must be allowed changes proportionable to the mixture. 

 Thus, if compound yellow light fall upon blue bise, the bise will 

 not appear perfectly yellow but rather green, because there are in the 

 yellow mixture many rays indued with green, and green being less 

 remote from the usual blue colour of bise than yellow, is the more 

 copiously reflected by it. 



In like manner, if any one of the prismatic colours, suppose red, 

 be intercepted, on design to try the asserted impossibility of repro- 

 ducing that colour out of the others which are pretermitted; it is 

 necessary, either that the colours be very well parted before the red 

 be intercepted, or that together with the red the neighbouring colours, 

 into which any red is secretly dispersed, (that is, the yellow, and per- 

 haps green too) be intercepted, or else, that allowance be made for 

 the emerging of so much red out of the yellow green, as may possibly 

 have been diffused, and scatteringly blended in those colours. And if 

 these things be observed, the new production of red, or any intercepted 

 colour will be found impossible. 



This I conceive is enough for an introduction to experiments of 

 this kind; which if any of the Eoyal Society shall be so curious as to 

 prosecute, I should be very glad to be informed with what success; 

 that, if anything seem to be defective, or to thwart this relation, I 

 may have an opportunity of giving further direction about it, or of 

 acknowledging my errors, if I have committed any. 



