DECOMPOSITION OF LIGHT. 23 



Thirdly, I conceived, that all the prolongations of the 

 radii of the dial to the red curve represented each a pro- 

 portional quantity of my red matter mentioned in the para- 

 graph before the preceding ; so that this dial is surrounded 

 by a red crescent to a certain point, whence it decreases ac- 

 cording to a given law. We must likewise admit a green 

 envelop, analogous to the preceding, and limited by the 

 curve of that colour; and lastly a violet envelop, within 

 the third curve. 



This supposed, if for each point of the dial we make a 

 mixture of colours corresponding to that point, we shall 

 have a series of tints in imperceptible gradation from one to 

 the other: which intone, place, and every other respect, 

 will be extremely analogous to the colours of the dial, that 

 I had previously traced conformably to the ideas of Newton, 

 and arc such, that the union of two diametrically opposite 

 to each other, will every where form a white identically the 

 same. 



This is a result which I offer as a farther probability 

 greatly in favour of my hypothesis of three colours. 



It is true, the dial constructed by the first method differs A little diffa - 

 a little from that by the last, as in this the purest red is lace of the 

 somewhat nearer the plaee of the orange, and the violet colours, 

 nearer that of the indigo. But, beside that this difference 

 ]< little in itself, it is supported by experience; for the re- 

 lation of colours in .general, and the progress of their ab- 

 sorption, appear to give some preference to the latter 

 method. 



Still I must repeat, that the observations I have here 

 made are only to shew the possibility of the thing; the 

 question can be decided only by the direct examination of 

 the rays of light on the spectrum in its simplest state, and 

 this remains for me to give. 



As few have the means of procuring this very simple Not easy to ob- 

 speetrum, and there is some difficulty in applying them, I ^^Matest 

 shall enter into this subject somewhat atlarge. This I con- si'mptic ity; and 

 eeive to be the more necessary, as few appear to have re- nave done 

 peat^d experiments of this kind since Newton, at least with 

 due precision. Treatises on optics indeed do not mention 

 {his repetition formally, many philosophers having attempt- 

 ed 



