208 Newton's Letters, Hypothesis and Experiments 



by light of any uniform colour made by a prism, I have seen 

 the lucid circles appear to about twenty in number, with many 

 dark ones between them, the colour of the lucid ones being 

 that of the light with which the glasses were illustrated. And 

 if the glasses were held between the eye and the prismatic co- 

 lours cast on a sheet of white paper, or if any prismatic colour 

 was directly trajected through the glasses to a sheet of paper 

 placed a little way behind, there would appear such other 

 rings of colour and darkness (in the first case between the 

 glasses, in the second on the paper) oppositely corresponding 

 to those which appeared by reflexion. I mean that whereas 

 by reflected light there appeared a black spot in the middle, 

 and then a coloured circle ; on the contrary, by transmitted 

 light, there appeared a coloured spot in the middle, then a 

 black circle; and so on, the diameters of the coloured circles 

 made by transmission equalling the diameters of the black 

 ones made by reflexion. 



Thus, I say the rings do and ought to appear when made 

 by uniform light, but in compound light it is otherwise. For 

 the rays which exhibit red and yellow, exciting, as I said, 

 larger pulses in the aether than those which make blue and 

 violet, and consequently making bigger circles in a certain 

 proportion, as I have manifoldly found they do, by illumina- 

 ting the glasses successively by the aforesaid colours of the 

 prism in a well-darkened room, without changing the position 

 of my eye or of the glasses ; hence the circles made by illumina- 

 ting the glasses with white light, ought not to appear black and 

 white by turns, as the circles made by illustrating the glasses 

 for instance with red light, appear red and black ; but the co- 

 lours which compound the white light must display themselves 

 by being reflected, the blue and violet nearer to the centre 

 than the red and yellow, whereby every lucid circle must be- 

 come violet in the inward verge, red in the outward, and of 

 intermediate colours in the intermediate parts, and be made 

 broader than before, spreading its colours both ways into those 

 spaces which I call the black rings, and which would here 

 appear black, were the red, yellow, blue, and violet, which 

 make the verges of the rings, taken out of the incident white 

 light which illustrates the glasses, and the green only left to 

 make the lucid rings. Suppose C B, G D, L F, P m, R n) 

 S X represent quadrants of the circles made in a dark room 

 by the very deepest prismatic red alone; and ij/3, y8, A<$, 7r^, 

 pv, <r£ the quadrants of like circles made also in a dark room, 

 by the very deepest prismatic violet alone ; and then if the 

 glasses be illuminated by open daylight, in which all sorts of 

 rays are blended, it is manifest that the first lucid ring will be 



