VOL. VIII.] PHILOSOPHICAL .TRANSACTIONS. 85 



pendicular to the rational or mathematical plane ii^y, by the hypothesis; there- 

 fore all the rays, passing from the object through the sights to the eye, are 

 parallel to the same right line, viz. to the ray passing through the globule and 

 hole O. Q. E. D. 



So?ne Considerations on Mr. Newton's Doctrine of Colours, and on the Effects of the 

 different Refractions of the Rays in Telescopical Glasses. In a Letter from 

 Paris. N° 96, p. 6O86. 



I have seen how Mr. Newton endeavours to maintain his new theory of 

 colours. It seems that the most important objection, which is made against him 

 by way of quaere is, that whether there be more than two sorts of colours. 

 For my part, I believe that an hypothesis, that should explain mechanically, 

 and by the nature of motion, the colours yellow and blue, would be sufficient 

 for all the rest, since those others, being only more deeply charged, (as appears 

 by the prisms of Mr. Hook,) produce the dark or deep red and blue, and that, 

 of these four all the other colours may be compounded. Neither do I see why 

 Mr. Newton does not content himself with the two colours yellow and blue ; 

 for it will be much more easy to find an hypothesis by motion, that may explain 

 these two differences, than for so many diversities as there are of other colours. 

 And till he has found this hypothesis, he has not taught us in what consists the 

 nature and difference of colours, but only this accident, (which is certainly YQ.Ty 

 considerable,) of their different refrangibility. 



As for the composition of white made by all the colours together, it may 

 possibly be, that yellow and blue might also be sufficient for that : which is 

 worth while to try ; and it may be done by the experiment which Mr. Newton 

 proposes by receiving against a wall of a darkened room the colours of the prism, 

 and to cast their reflected light on white paper. Here you must hinder the 

 colours of the extremities, viz. the red and purple, from striking against the 

 wall, and leave only the intermediate colours, yellow, green, and blue, to see 

 whether the light of these alone would not make the paper appear white, as 

 well as when they all give light. I even doubt whether the lightest place of the 

 yellow colour may not alone produce that effect, and I mean to try it at the 

 first conveniency ; for this thought never came into my mind but just now. 

 Mean time you may see, that if these experiments succeed, it can no more be 

 said that all the colours are necessary to compound white, and that it is very 

 probable that all the rest are nothing but degrees of yellow and blue, more or 

 less charged. 



Lastly, touching the effect of the different refractions of the rays in telesco- 

 pical glasses ; it is certain that experience agrees not with what Mr. Newton 



