ic8 Inquiries ■into- Cohukid Light. 



bjue, as the one or the other p>eclominated iu the compo- 

 fition. 



But to put this matter out of all doubt, the fa£l comes out 

 on experiment, that when the gradations of the colour take 

 fuch an arrano;cment that there is no interfeftion of the yel- 

 low orbicular miages with ihoic of the blue, and fo no coa- 

 lefcence ot thefe colours, //'^Tt; /.? wo _gT<?r/z. 

 , Obferv. iv. part i. book ii. p. 174. Sir Ifaac Newton fays, 

 *' the c-olours reckoned in their order from the centre were, 

 black, blue, lulnte, yellow, red ; here the blue and yellow 

 not intericAing orcoalefciug, but feparated by an intervening 

 white, there was «y green in this gradation of colours : if 

 they had ap[)roached iomewhat near to an interfeftioii of 

 their circles, there might have been, as above, a whitifli or 

 willow-green bordered with vellowifli and blucifh green. 

 Tliefan;re fact is dated in Obfervation ix. p. 181 : the~order 

 of this gradation was, " violet, blue, white, yellow, red." 

 Here again an intervening fpace of white excludes the exill- 

 ence of green. The fame fact oi' an' inierK'eni/ig ichite be- 

 tween the yellows and the blues, excluding the green, comes 

 out in fome experiments and obfervalions made bv G. W. J.* 

 in addition to thole made by bir Ifaac Newton, where, in 

 p. 99. he itate?, that " diluted purple and blue hues appear 

 'completing, with the external yellow and red, and an tnlcr- 

 vening white, thefe formations of thefe fringes." I will 

 ■venttire to add, in confirmation of all this, one amongft fe- 

 Kejal obfervations which I made on thefe fads. Viewing, 

 through a prifm, the folar light as it came through a falh 

 window, and taking the fpeftrum in the line of refracSlion as 

 it came from above, the following circumftances appeared : — 

 The frames of the falh were dark, and gradations of colours 

 proceeded from them. The gradations of blue on the upper 

 fide; thofe of the red, orange, yellow, from the lower' iide. 

 The gradations proceeded from the upper fide iii this order — 

 deep, blue, and, in fuccefiion, the feveral lighter tints or hues 

 of blue till they vanifhed in the folar light. From the under 

 part they proceeded in this order — deep red, then a brighter, 

 going into orange, and the orange fucceffively brightening 

 into yellow, which melted oft' into the folar light : no gra- 

 dations of blue iucceeded cither order, bccaufe there was 

 no going off of light into fhade when the fpectrum was thus 

 tranfparent to the folar light ; and as there was no blue to in- 

 termix with thelafl: yellow, there was no green. In proof that 

 this is the reafon, it may be obferved, that if the light itfelf 



* A '.-cry ingenious work publiJhed b; Cadill 1799. 



through 



