<(^ Inquiries into Coloured Light. 



feding each other, that the point of interfcellon is hardly 

 perceptible to a common eye unaflfifted, if at all. Although, 

 therefore, the centres of thefe circles may approach to each 

 other at an infinitely hnall diftance ; yet they arc placed under 

 different refiaftionsj' and nnift, ofcourfe, give a fuccceding 

 tint more refrafted than the preceding : and as thus through- 

 out thefpace of the commonly called homogeneous colour, fo 

 muft the indifcriminate feries of refraftions, and ot the inter- 

 fccling images of the fun, proceed gradatim, and not per 

 faltum^ into'the next fpace of the next primary colour; and 



'to through that into the next ; and in like manner throughout 

 the whole. The angle of rofrat^tion at the point where the 

 fpace in the fpeiifrum, which contains the red, is fuppofed to 

 end, exceeds tliat which is on the outfide of the fame fpace, 

 where it commence*, in a much greater degree than it doth the 

 next contiguous and continuous feries of angles of refraction of 

 thefpace which contains the orange. And the fame holds good 

 of the laft angle of refra£lion at the point where the orange 

 ends, or is fuppofed to end, and where the yellow com- 

 mences, or is fuppofed to commence; and fo through all the 

 c;vadations of colours. Sir Ifaac Newton, in the hypothefis 

 of his theorem inflituted for experiment, fo dates it. As 

 therefore the angles of refraction at the centres of the innu- 



• merable* circles or orbicular images of the fun in the prif- 

 inatic fpeflrum, as ftated by Sir Ifaac Newton, which form 

 any one of the principal colours, homogeneous as they have 

 been called, thus diBer in their degrees, fo mnft the tints in 

 each fuch colour tliU'er in a forics of gradations ; and cannot 

 therefore, however they may to a tranfient or undifcrimi- 

 natinsr view appear, be ablblutely homogeneous : " for, the 

 light which I here call homogeneous (fays Sir Ifiiac Newton) 

 being not homogencal, there ought to arife fome little change 

 of colours from its heterogeneity f." The red, by fuch a fuc- 

 ceflive feries of lints, is heightened towards and expanded 

 into the orange; the orange, by a like fuccellion of tints, into 

 the yellow ; and the yellow, in like manner, into the white. 

 . As thefe coloured lights on this end of the fpe<Slrum 

 heighten by gradations of tints more and more illumined, 

 as if purging themfelves from the fufl'ufion of colour into 

 pure light : fo tfe blues at the other end of the fpettrum, by 

 a like gradation of tints, or rather hues, deeper and deeper, 

 weaker and weaker, go. off into darknefs, in " a continued 

 feries, according tc iheir degree of refrangibility |." 



♦ P^ide fig. ic. o' pl^tc 3. hook i. part i. Newton's Optics. 

 + Newton's Optics, hook i. part xii. ptop. II. p. 107. 

 J. Ni'wton's 0[)tics, p. 31. 



6 Having 



