688 PHILOSOPHICAL TRANSACTIONS. [aNNOIG^I. 



the colours are projected; which in Q constitute whiteness, but are red and 

 yellow in R, r, and ^, and blue and purple in P, p, and tt. 



If you proceed further to try the impossibility of changing any uncompounded 

 colour, (which I have asserted in the 3d and 13th propositions) it is requisite 

 that the room be made very dark, least any scattering light mixing with the co- 

 lour disturb and allay it, and render it compound, contrary to the design of the 

 experiment. It is also requisite, that there be a perfecter separation of the co- 

 lours than, after the manner above described, can be made by the refraction of 

 one single prism, and how to make such further separations, will scarcely be diffi- 

 cult to them that consider the discovered laws of refractions. 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 inter- 

 cepted, on design to try the asserted impossibility of reproducing 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 w ith the red 

 the neighbouring colours, into which any red is secretly dispersed, (that is, the 

 yellow, and perhaps 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 Royal Society shall be so curious as to prosecute, I should 

 be very glad to be informed with what success; that, if any thing seem to be 

 defective, or to thwart this relation, I may have an opportunity of giving fur- 

 ther direction about it, or of acknowledging my errors, if I have committed 

 any. 



An Account of some Booh. N° 80, p. 3088. 



I. Beschriving der Oost Indische Kusten, Malabar, Coromandel, Ceylon, &c. 

 Door Philippus Baldaeus. T. Amsterdam. 1672, in fol. 



The author of this recent history, an active Dutch minister, having lived 



