But, fuppofing that ^//Colours mightjaccordihg to this ex' 
perimeot^be produced out of Y^r^ by mixture , yet it follo w^ 
uotj that thofe two are the only Original coloms^ and that fo^ 
a double reafon, Firji^ becaufe thofe two are not themfelve^ 
Original colours^ but compounded ofothers 5 there being 00 
liquor nor any other body in nature, whofe colour in Day. h'ght 
is wholly un-compounded^ And ^^^jw^ becaufe^ though thofe 
two were Originalj and all others might be compounded of 
them^ yet it follows not, that they cannot be otherwife prodip 
ced. For I faid^ that they had a double Origin, the fame Co- 
lours to fenfe being in fome cafes compounded and in others 
un compounded ; and fufficiently declared in my third and 
fourth Propofitions, and in the Conclnfionj by what Properties 
the one might be known and diftinguilh'c from the other, Butj 
becaufe I fufpe<9:by fome Cireumfhnces, that ihQ DiftinBton 
might not be rightly apprehended, I fhall once more declare 
it, and further explain it by Examples. 
That Colour i$ Primary or Original^ which cannot by any 
Aft be changed, and whofe Rays are not alike refrangible i 
And that Compounded^ which is changeable into other colours^ 
and whofe Rays are not alil^ refrangible. For tnfiance^ to 
know, whether the colour of any Green objeftbe compeofi^ 
ded or not, view it through a Primej and if it appear confufei. 
and the edges tinged with^/w, TelloWy Ot any variety of 
ther colours, then is that Cw« compounded of fuch coloors 
as at its edges emerge out of it : But if it Sippczr diJiinSl^ and 
well defin'dj and entirely Greco to the very^dges, withoot 
any other colours emergingjit is of an Original and on-cora^ 
pounded Green* In likemanner^ if a refradied beaai of light, 
being caft on a white wall^ exhibit a Grmi colour, to know 
whether that be compounded, refradi the beam with an in« 
terpofed Prifme 5 and if youfindany DifFormicy in the refra- 
dtions, aiid the Green be transfbrm'd into Biem^ TeBowflv any 
varietj'yof other colours, you may conclude Jthat it was com^ 
pounded of thofe which emerge : But if the Refractions be 
uniform, andtheGw;^ perfift without any change of colour, 
then is it Original and un compounded* Andthe reafon why 
I icall it fo, is, becaufe a Gree?i indued with foch properties can- 
not be produced by any miKing of other colours. 
