Inquiries into Coloured Light. 43 



The procefs of this theorem is founded on the experiments 

 aftually made by Sir Ifaac Newton, and on fome further 

 experiments and realoning, which his quzeries fuggeft. 



I wifli this imperfect attempt may excite fonie real philo- 

 fophers to take up this point of incjuiry. 



IT appearing from Dr. Herfchel's obfervations, publiflied 

 in tlie Philofophical Tranlatlions 1796, that the folar hght 

 docs not proceed from the fun as an igneous body, but appa- 

 rently from inflammable and inflamed vapours floating on 

 the furface of its atmofphere; and it having been long known 

 that this white lucid lieht could be decompofed into a num- 

 ber of coloured rays, each homogeneous, as has been fup- 

 pofed ; each " originally endued," as Sir Ifaac Newton fays, 

 "with its refpeclive colour;" or, as he otherwifeexprelfes the 

 fame faft *, " with that which each is originally difpofed to 

 exhibit ;" it occurred to my mind, on reading this in the year 

 1797, that thefe obfervations of Dr. Ilerfchcl, if finally found 

 to be true in nature, and followed up by an induftion of 

 combinincT fa6ls, might lead to a difcovery of that property of 

 light which hitherto appeared to me to be inexplicable, at 

 leaft unexplained, viz. that every the minuteft ray of which 

 it confills is a compound of feven, or three, principal primary 

 homogeneous coloured rays, each originally endued with 

 its rcfpeftive colour, as conftituent elements of this lucid 

 white light. 



It occurred to me, that if Jimilnr coloured lights, arifing 

 from the aerial inflamed vapours, or flames of bodies com- 

 burcd in our terreftrial atmofphere, flioold bo found to obferve 

 the fame rcfraftioos, and by thefe refraAions, as they never 

 are purely homogeneous, fliould in their decompofition ob- 

 ferve and be aflected by the fame laws as operate on the folar 

 light ; the folar light may, by direft analogy, be fuppofcd to 

 be only a compound of inflamed vapours taking the refpec- 

 tlve colours of their flame, and being endued with their re- 

 fpeftive rcfradions, according to fuch altraftions as the ro- 

 fpeclive fubflanccs from which they arife are liable to. Whilft 

 I conlidcred this, I recolleAed that I had read in, and learned 

 from. Sir Ifaac Newton, fpeaking of flame, according to an 

 expreflTion which he ufed at that time, " as fmoke red hot," 

 that, " accordnig to the nature of the fmoke, the flame is of 



• Tlitrc arc fome ph.^nonrcn* in the difl'crrtit colours of the fixt (\ars 

 which fttm to indicntc thai the coloured liglit of tlicir lyttrni may differ 

 from thdt of the foUi one. 



various 



