Definitions, 
1 1 call that Light homogeoeal, fioiilar utiifora:!^ whofe 
rays arc equally rcfraogible. 
%. And that hetcrogcocal^whofc rays are unequally rcfraa^^ 
gjble. 
Note.Thcre are but three affedlioos of Light in which I have 
pbfcrvcd its rays to differ* t'/^Aefrangibility, Eleflexibility, 
and Colors and thofe rays which agree in refrangibility a^ 
gree alfo in the other two,and therefore may well be defined 
bomogeneal » efpecially fince men ufually call thofc things ho* 
inogcncaljWbich arc fo in all qualities that come uudcr their 
jknowledg, though in other qualities that their knowlcdgexi 
tends not to there may poffibfy be feme heterogeneity* 
5 , Thofe colors I call firaple, or homogeneal, which are ex?* 
hibiced by homogeneal light. 
4. And thofe compound or heterogeneaI,which are exhibi- 
ted by heterogeneal light. 
5* Oificrent colors I call not only the more eminent (pc* 
cies,red,yellow, green, blew, purple, but all other the minu- 
t eft gradations ; much after the fame manner that not only 
the more eminent degrees in Mufick, but all the leaft gradatit 
ons are eftcemdd different founds. 
Fropofitiom. 
I. The Sun's light confifts of rays differing by indefinite 
degrees of Kefrangibility. 
a. Rays which differ in rcfrangibility , when parted from 
one another do proportionally differ in the colors which they 
exhibit. Thefe two Propofitions arc matter of fad. 
3. There arc as many fimplc or homogeneal colors as de« 
' grees of rcfrangibility. For, to every degree of refrangibi- 
lity belongs a different color,by Prop. 2. And that color is Gmpic 
by Def. I, and 3. 
^ 4. Whiteacfs in all refpefts like that of the Sun's immediate 
light and of all the ufiial objefts of our (enfts cannot be com- 
pounded of two fimplc colors alone. For fuch a compofitioa 
muft be made by rays that have only two degrees of refran- 
gibility,by Def. i. and 3 j and therefore it cannot be like that 
of the Sunslightjby Prop, i • Nor,for the fame reafon, like that 
of ordinary white objeits. 
StWhitencfs 
