Sect.VIL] Optics. 63 



takes. His idea, that the colours of bodies depend 

 on the magnitude of their elementary particles, 

 has, it is believed, at present, few advocates. Aiter 

 him this subject was considered, though in a more 

 practical way, and with reference to the art of 

 dyeing, by several French philosophers ; especially 

 by Dufay, "Hellot, and Macqaer, who conducted 

 their inquiries with great ability, pains, and per- 

 severance, at the national expense. More reccntiv, 

 Mr. Delaval, of Great Britain, rehning on the con- 

 jectures of Newton, attempted to deduce the 

 varieties of colour from the different densities and 

 inflammability of bodies. I'his w^ork was for some 

 time popular; but appears lately to liave given 

 way, in the public opinion, to the more enlighten- 

 ed and correct philosophy delivered on this sul)ject 

 by M. Berthollet, and Dr. Bancroft, who ibund 

 the whole doctrine of colours on ehemicat princi- 

 ples — supposing that particular bodies redect, trans- 

 mit, or absorb particular rays of light, in conse- 

 quence of certain affinities, or elective attractions^ 

 existing between the differently coloured matters, 

 and the different rays of light, reflected, transmit- 

 ted, absorbed, or made latent*. 



But the discoveries and improvements in tiie 

 construction of optical instruments^ which the last 

 age produced, are still more brilliant and interest- 

 ing than any hitherto mentioned. Much was 

 done, during the period in question, in the im- 

 provement of Telescopes. The Refracting Tele- 

 scope was first in use. In this instrument no sig- 



* See Experimaital Researches conceiminu; the Philo.sophj/ of Pcr- 

 njancnt Colours, by Edward Bancroft, M. D.l^. R. S. 179'^- 



