( 40C4 ) 
A Series of Q^tts propounded by Mr. Ifaac Newton, to be de- 
termind ky Experiments , pofitively and direSlly concluding his 
new Theory of Light and Colours and here recommended te the 
InduUry of the Lovers of Experimental Phikfophy, as they were 
generoufly imparted to the Publtjher in a Letter of the (aid Mr. 
Newtons of July 8 . 1 67 2 ♦ 
IN the mean while give me leave, Sir, to infiauatejthat I can- 
not think it effeAual for determinfng truth, to examin the 
feveral waies by which .Phaspomena may be explained, unlefs 
where there cau be a perfect enumeration of all thole waies. 
' You knoWjthe properMethod for inqumng after the properties 
of things isjto deduce thejxi frpm E5tperiments«And 1 told you, 
that the Theory,which I propounded, was evinced to mc, not 
by inferring 'tis, thusbecaufe not otherwjfe , that is, not by 
deducing it only from a confutation of contrary fuppofitions , 
but by deriving it from Experiments concluding pofitively 
anddire£Hy> The way therefore to examin it is, byconfi- 
dcring^ whether the Experiments which I propound do prove 
thofe parts of the Theory, to w.hich they are applyed 5 or by 
prqfecuting other Experiments which the Theory may fug- 
geft for its examination. And this I would have done in a due 
Method 5 the Laws of RefraUion being throughly inquired in- 
to and determined before the nature of Colours betakeninto 
confideratiori. It may not be amifs to proceed according to 
the Series of thefe ^£ries $ which I could wifli were determi* 
ned by the Event of proper Experiments • declared by thofe 
that may have the curiofity to examin them. 
1. Whether rays, that are <«/i^e incident on the fame M^"^/- 
um^ hdiVQ unequal tQivzSi\on%'y and how great are the inequa- 
lities of their refraditions at any incidence? w 
2. What is the Law according to which each ray is more 
©r lefi refracted 5 whether it be that the fame ray is ever re- 
fraSed according to the fame r^^^o of the fines of incidence 
and fefra(Stion ; and divers r3yf,according to divers ratio's'^ or 
that- the refra<3:ion of each ray is greater or lels withcutany 
certain rule > That is , whether each ray have a certain de* 
gree of refrangibility according to which its rcfradtion is per* 
tormed 5 or is refraded without that regularity/ 
3* Where- 
