HS CONSIDERATIONS ON COLOURS. , 



hand, of various nalures and of all colours, whether yellow, 

 orange, red, or green, blue and violet, owed their coloured 



Laws. appearance to the following laws: 1(1, each of the bodies 



always abforbed the rays that were complementary to the pre- 

 dominant colour: 2dly, in fome the abforption included, be- 

 fide the complementary fpecies, others collateral to this 

 fpecies, and more or lefs numerous : Sdly, the deeper a 

 colour is, the fewer fpecies of rays it reflects. 



Relates to che- It is to be underftood that mixed colours are not here fpoken 



™ Ca d<; OI not me-°^ ^ ui on '^ tno * e ,nat * orm a homogeneal compound, or a 

 chanicat mix- true combination, in the fenfe in which chemifts ufe this word, 

 tures. ]\j- or mu ft t j lc co I our reflected from the interior of the molecules, 



fufceptible of light or deep tints, be confounded with the 

 light reflected from the anterior furface of bodies: and though 

 this mixes more or lefs with the proper colour, it is eafy to 

 diminith its effects, and difcriminate them in the experiments. 

 Predominant Another remark proper to be made, is, that the expreflion 



predominant colour muft not be fuppofed to imply, that the 

 rays of this colour aie more abundant than the reft, which 

 would be a miftake. Several fpecies of rays may exift to- 

 gether in the pencil producing the colour, without any one 

 fpecies being for this reafon more abundant. Strictly fpeak- 

 ing, all the elements of the pencil are diffimilar; and con- 

 fequently no one exifts in it in greater quantity. But the 

 general tone of colour remains analogous to that of the rays 

 ityled predominant ; for which reafon it is well to retain the 

 term, provided it be not taken in an exaggerated fenfe. 

 Tranfparent f h e author has likewife obferved tranfparent bodies, fuch 



fame law of as c-'loured glafs of different forts, and liquors contained in a 

 abforption. bottle with two broad parallel tides. For thefe he found the 



fame law of abforption as for opake bodies, but ftill more 

 marked, and free from all doubt. 

 Its nmdifica- This law is conftant and regular. It depends on the nature 



tJ - (Uls * of the body receiving the light, its denfity, and its thicknefs. 



It is likewife modified by the intenfily of the light of the il- 

 luminating body, and the kind of rays that compote this 

 light. 

 Progrefs of the The abforption always commences with the rays moll, 

 abforprion of oppofite to the predominant colour of the body illumined. It 

 goes on to thofe which tonic next in the (peclrum : and thus 

 proceeds regularly from one order of rays to the next in fuc- 



cefiion, 



