[ 120 ] 



'* fuppofed," fay Fourcroy, " that three of thefe colours, the 

 " red, yellow and blue, were fimple ; and that the other four 

 '• were formed each of its two neighbours; that is, the orange 

 " from the r^d and yellow, the green from the yellow and blue, 

 " the Indigo from the blue and violet, and the violet from the 

 " red and indigo. But this fuppofition has never been proved." 

 See his Philofophy of Chcm. ch. i. § 3. Belides that this is a 

 mere hypothefis, unfupported by any fadl, as Fourcroy obferves, 

 we remark, that it is in itfelf inadequate ; iH, becaufe in the folar 

 fpedlrum. the red and indigo are not tieighbriuring colours but 

 are almoft at the greateft poflible diflance from each other, sdly, 

 According to this hypothefis, indigo is compofed of blue and 

 violet ; btit violet is compofed of red and indigo ; indigo therefore 

 is compofed of red, blue and indigo, that is, indigo itfelf is one 

 of its own elTential ingredients, which is abfurd. 



The experiments of the prifm feem to eftablifli, in a very 

 clear manner, the exiftence of feven original and uncompounded 

 colours ; and though green, for inftancC; may be compounded of 

 blue and yellow, yet it does not diredtly follow from thence, that it 

 always is fo adually compounded. Accordingly Newton tells us, 

 that green may be exhibited in two different ways, either by pri- 

 mitive, green making rays, which are fimple and not refolvable 

 by any reflcdion or refradion into different rays ; or by a com- 

 pofition of blue and yellow rays, which are differently refrangible, 

 and which therefore after their union, may again be fepa- 



rated 



