Mechanical Pldlosophy. 53 



vision explained by Mr. Melville, M. Boltguer, 

 and others. 



The principles and laws of colours have also 

 been much better understood since the commence- 

 ment of the eighteenth century than before. On 

 this subject it seems now to be generally agreed 

 that the immortal Newton fell into essential mis- 

 takes. His idea, that the colours of bodies de- 

 pend on the magnitude of their elementary par- 

 ticles, has, it is believed, at present, fev/ advo- 

 cates. After him this subject was considered, 

 though in a more practical way, and with refer- 

 ence to the art of dyeings by several French 

 philosophers, especially by Dqfay, Hellot, and 

 Macquer, who conducted their inquiries with 

 great ability, pains, and perseverance, at the na- 

 tional expense. More recently, Mr. Delaval, 

 of Great Britain, refining on the conjectures of 

 Newton, attempted to deduce the varieties of co- 

 lour from the different densities and Inflammability 

 of bodies. This work was for some time popular, 

 but appears lately to have given way, in the public 

 opinion, to the more enlightened and correct phi- 

 losophy delivered on this subject by M. Berthol- 

 jlet, and Dr. Bancroft, who found the whole 

 doctrine of colours on chemical principles— sup- 

 posing that particular bodies reflect, transmit, or 

 absorb particular rays of light, in consequence of 

 certain affinities, or elective attractions, existing 

 between the differently coloured matters, and the 

 different rays of light, reflected, transmitted, ab- 

 sorbed, or made latent.' 



But the discoveries and improvements in the 

 construction of optical Instruments, which the last 

 age produced, are still more brilliant and interest- 



S See Experimental Researches concerning the Philosophy of Permanent 



Colours^ by Edward Bancroft, M. D. F. R. S. 1794. 



