$4 Experimetits and Ohjlrvations on Light. 



than the exiftence of different forts of rays, which may not eafily be fuppofed fo numerous, 

 and capable of fo regular a difperfion. Thus modification is eft;ablifhed,^as well as fcpa- 

 ration, and thefe principles of condition and formation alone fuit the phenomena. The 

 fringes before obferved, require complete fets of the different coloured rays to iffue at th* 

 fame time, from each interval or point of paffage of the medium. For this purpofe an ap- 

 propriate arrangement is required of the rays, if of originally different forts in different 

 paffages, and only mixed in the white light, left a nearer red fliould be more infledled than 

 a further blue, and the like, and this arrangement will even then agree with only one 

 ilation of the inflefting body ; but this ftation is indifferent in producing the phaenomena. 

 A confufed mixture therefore, of rays, is inconfiftent with the phxnotflena, no collateral 

 arrangement will anfwer ; and if all the different rays mull be confidcred as pafiing 

 through all the intervals of the medium, they cannot all iffue from, or be returned at the 

 fame time, to the fame place as the phenomena require. By fuppofing, however, that the 

 time of fuccefiion of all the rays in the fame paffages is imperceptible to fenfe, then the 

 hypothefis of fimple feparation, and original diftinftnefs of the rays, may anfwer for thefe 

 phsenomena, as well as that of feparation and modification ; but as they will both then 

 anfwer equally well, other the general phenomena can alone determine which is true, and 

 by them they mufl: be judged. 



Omitting, however, all confideration of thefe two hypothefes, it is clear, that in the 

 preceding obfervations concerning inflexions, Newton is miftaken as to all the moft im- 

 portant points. He has upon different occafions, endeavoured to eftablifli a power alto- 

 gether repulfive, or a power changed at different diftances from attradlive to repulfive. 

 This repulfive power has been always hitherto ufed in philofophy, to account for the re- 

 flexions of light, and as it is clearly (hewn not to exift, another manner of accounting for 

 refleXion is to be fought for. 



The concluding obfervations of the work are general. It is ftated among other things, 

 that the Newtonian dodlrine of light and colours is unfounded as to both its principles ; 

 the conftitution of folar light (queftioned indeed in the laft obfervation), and the fits 

 of eafy tranfmiffion and refleftion of the rays. The fame Author is preparing to 

 publifh, Obfervations concerning the Colours of thin Plates, (hewing the phenomena 

 to be merely inflexions of light, that the Newtonian fits of eafy tranfmiffion and refleXion 

 have no exiftence, and that Newton's doXrine of the grounds of the colours of natural 

 bodies is unfounded. » 



The obfervations of Newtoti in the above work marked with the numerical figures, 

 are printed with a reduced margin ; the new obfervations marked with the letters of the 

 Greek alphabet, are printed with a full margin. 



Singular 



