170 Ddaval. [Book III. 



which Teemed multiplied before, now appeared but 



The laft, though not lead fuccefsful adventurer in 

 this branch of fcience, is Mr. Delaval, who, in a paper 

 read before the Philofophical Society of Manchefter 

 in 1784, has endeavoured, with great ingenuity, to ex- 

 plain the permanent colours of opake bodies. The 

 majority of thofe philofophers, who have treated of 

 t and colours, h.ive, he obferves, fuppofed that cer- 

 t'i ' odies or furfaces reflected only one kind of rays, 

 a:id therefore exhibited the phenomena of colours; on 

 tie contrary, Mr. Delaval, by a variety of well con- 

 ducted experiments, evinced, that colours are exhibit- 

 ed, not by rerkfted^ but by tranfmitted light. This 

 he proved by covering coloured glaffes and other tranf- 

 parent coloured media, on the further furface, with 

 fome fubftance perfectly opake, when he found they 

 reflected no colour, but appeared perfectly black. He 

 concludes, therefore, as the fibres or bafes of all vege- 

 table, mineral, and animal fubftances are found, when 

 cleared of heterogeneous matters, to be perfectly 

 white, that die rays of light are in fact reflected from 

 thefe white particles, through coloured media, with 

 which they are covered ; that thefe media ferve to in- 

 tercept and impede certain rays in their.pafTage through 

 them, while, a free paflage being left to others, they 

 exhibit, according to thefe circumftances, different co- 

 lours. This he illuftrates by the fact remarked by 

 Dr. Halley, who, in diving deep into the fea, found 

 that the upper part of his hand, when extended into 

 the water from the diving b-11, reflected a deep red 

 colour, while the under part appeared perfectly green. 

 The conclufion is, that the more refrangible rays were 

 intercepted and reflected by particles contained in the 



fea- water. 



