208 
tions. Farther, we 'have seen, that the chemical 
changes of decomposition and combination are effect- 
ed by invisible light, in which changes the luminous 
or visible portion has no necessary share. 
484. But in the operations of invisible light on bo- 
dies, we have traced a close analogy to the actions 
of the electric fluid ; and may we not extend this 
analogy to those affections of the luminous or colori- 
fic rays, which enable bodies to present all the end- 
less modifications of colour ? Such an idea, however, 
at once presupposes the exertion of an attractive force 
between bodies and this portion of light ; and should 
the circumstances already stated be deemed insuffi- 
cient to establish this fact, the phenomena afforded 
by inflection seem decisive of the question. It is well 
known, that if different bodies be made to approach 
a beam of light, as it enters a darkened room through 
a small hole in the window, the light will be drawn out 
of its rectilinear course. Sir Isaac Newton found that 
this effect was produced not only on the entire beam, 
but, in different degrees, on the different colorific rays; 
forthe fringed shadows of bodies held in red light were 
larger than those of bodies held in green light ; and 
these last were still larger than those of bodies held in 
the violet rays : so that the same body, says Newton, 
acted upon the red, or least refrangible ray, at a 
greater distance than on the violet, and by those ac- 
tions disposed the red light into larger fringes, and 
the violet into smaller, and the lights of intermediate 
colours into fringes of intermediate sizes *. Surely 
* Optics, 13. Hi. 
