( 3o87 ) 
If you proceed further to try the impoffibiHty of changiflg any 
uncompounded colour (which I have afferted in the third and 
thirteenth PropofitionSj) 'thrcquifite that the Room be made ve* 
ry dark, leaft any fcattering hghtjmixing with the colour^difturb 
and allay it, and render it compound^ contrary to thedefignof 
the Experiment. 'Tis aifo requifite, that tliere be a perfeder re- 
paration of the Colours^ thaDjafter the manner above defcribed, 
can be made by the Refradlion of one fingle Prifme^ and how to 
make fuch further feparations^will fcarce be difficult to them^that 
confider the difcovered laws of Refradlions. But if tryal fliall 
be made with colours not throughly leparaterfj there muft be al- 
lowed changes proportionable to the mixture^ Thus if com* 
pound Yellow light fall upon Blew Bifey the Bile "w'lW not appear 
perfeftly yellowj but rather green, becaufe there are in the yel- 
low mixture many rays inciued with green, and Green being lefs 
remote from the ufual blew colour of Bife than yelloWj is the 
more copioufly refledled by ir^ 
In like manner, if any one of the Prifmatick colours, fuppofe 
Red, be intercepted^ oudefignto try the afferted impoffibility 
of reproducing that Colour out of the others v^bich are preter- 
mitted ; *tis neceflary^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 fecretly difperfed^,, 
(thatis, theyellow, and perhaps green too) be intercepted, or 
clfe, that allowance be madefortheemergingoffo much red out 
of the yellow green, as may poffibly have been diffufed^ and - 
fcatteringly blended in thofe colours. And if thefe things be ob- 
fervedj the new Produdlion of Red, or any intercepted colour 
will be found impoflible. 
ThiSjI conceive, is enough for an Introdudion to Experiments 
of this kind ; which if any of the J{.Sm€ty (hall be fo curious as to 
profecutCjI fliould be very glad to be informed with what fucce(s: 
That,if any thing leem to be defeftive,or to thwart this relation, I 
may have an opportunity of giving further diredtion about it, or 
of acknowledging my errors» if 1 have committed any. 
^Si^/iir this Learned and very Ingenious Better i which having 
bttnhy that J Ihfir to jis Compa?2y^ before whom it was read, with 
much applaufe committed to the confideration of fome of their 
FellowSjWell verfed in this argument, the Reader may poffibly in 
an other Tr^S be informed of fome report given in upon this ty\U 
courfc. ' J:i 
