( 6ioB ) 
AnEoctracfofMrAf^ncNcwtonsLeiter^ mitten to the Ptihli* 
Jher from Cambridge April 5. 1673. concerning the Number 
of Colors^ and the Necejjzty of mixing them all for the pro- 
dnction <jjf White § alfo touching the Caufe why a Pillure caJi 
^hy GlaJJes into a darkned room appears fo difiin& notwithjland' 
ing its Irregular refra'clion : (Which Letter^ being an Imme- 
diat anfwer to that fromPans^ printed N^'.gS.p^SoSS. oftheje 
Tra6ts, Jhould afo^ if it had not b^en miflaid^ have immedi- 
ately followed the fame.) 
IT feems to me^that N, takes an imj^roper way of examining 
the nature of C(7/<?r/,whilft he proceeds upon coropoouding 
thofe that are already compounded 3 as he doth in the former 
part of his Letter* ^ Perhaps he would fooner fatisfie himfelf 
by refolving Light into Colors^ as far as may be done by Art, 
and then by examining the properties of thofe colors apart 
and afterwards by trying theeffeds of re-conjoining two or 
more orall ofthofe^ andlaftly, by fcparadng them again to 
examines whM changes that re conjunftion had wrought in 
them* This,I confcfh., will prove a tedious and d ifBcult task 
to do it as it ought to be done 5 but I could not be fatisfied, 
till I had gone through it* However,! only propound it,and 
leave every man to his own method. 
As to the Contents of his Letter,! conc€ive,my former An- 
fwer to the^^^re about the Number of Colors is fufBcienc, which 
was to this etfia 5 That all Colors cannot praftically be deri- 
ved out of the Yellow and Blervy and confcquently that thofe 
Hypotkefes are groundlefs which imply they may. If you ask, 
What colors cannot be derived out of yellow blew} A ^n- 
fwer^none of all thofe which I defin'd to be Original j and if 
he can fliew by experiment^how they mayj will acknowledge 
my feif io ao error. Mor is it eafier to frame an Hypothecs by 
afluroing only two Original colors rather than an indefioit 
variety ; uolefs it be eafier to fuppofe, that there are but two 
figar€s,fizts and degrees of velocity or force of the iEthereai 
corpulcles or pulfes^rather than indefinit Variety ^ which cer- 
raioiy would be a harfh fuppofition. No man wonders at the 
lodcfiQir variety of Waves of theSca,or of fands on the ihorei 
bur, 
