DECOMPOSITION: OF LIGHT. Si 



erected an ordinate, and afterward drawn the arbitrary In- 

 dined line a d, then b g cutting the former in c, and -lastly 

 e h cutting the preceding in /. I suppose, that the modi, 

 ficafions of the red rays, on which their different refrangi- 

 bility depends, are represented by the ordinates correspond- 

 ing fo the line a d: these quantities express nothing relative 

 either to the velocity of the rays, or the magnitude of their 

 particles ; perhaps they may have a relation to their density, 

 or to any other quality whatever that constitutes their dif- 

 ference. In Newton's system of seven classes of primitifs 

 colours, there are likewise red rays differently refrangible; 

 this therefore Is not a difficulty peculiar to the state of things 

 I am examining. In like manner the ordinates of the line 

 g g will be the modifications of the green ; and those of the 

 line h c the modifications of the violet. Hence it is evideat r 

 that the first division of colours from a to b will be red 

 alone; that it will be followed by a mixture or combination 

 of green and red from b to c, in which the quantity of the 

 latter will predominate, and give orange; after which an- 

 other mixture of red and green will proceed from c to d-, in 

 which the green will predominate more and more, forming 

 yellow ; then from d to e will be green alone; frome tof the 

 mixture of green and violet that produces blue; from/ to g 

 thr mixture producing indigo; and lastly from g to h pun; 

 > iolet. 



But another very striking property of the spectrum, Accounts for 

 which has net hitherto been explained, is the greater bright- -* e g^ 016 ** 

 r.e«3 of the yellow compared with the rest. This proceeds 

 evidently in my figure from being the sum of the light of the 

 red and or the green. In the blue too there is an augmeu- Blue next in 

 -tatioa of light by the union of the green and violet; but de | ree of H S ht ' 

 the effect is much less than in the preceding instance, both 

 from the nature of those colours, and their extent, though 

 there is some trace of it in the spectrum when properly dis- 

 played. 



By this figure, however, I do not pretend fo exhibit any 

 thing more than what may possibly happen. For this rea- 

 son I have limited the ordinates of each colour by a right 

 line merely; for as the law of their progression is notknown 

 so that it is impossible to give the precise curve, 1 have 

 adopted the simplest line as sufficient for my purpose. 



The 



