35G On the Refraction of Light. 



lead, pierced with holes of nearly a line in diameter, at equal distan- 

 ces from one another, (about an inch,) and in the same line. The 

 bases of the pyramids, formed by the insulated colors, being received 

 on paper, were found to occupy exactly the same spaces, and to be 

 equal to one another.* The rays of the different colors are, there- 

 fore, all equally diffrangible. 



The shadows of bodies in homogeneous light, instead of being 

 fringed with colors, as in compound light, are bordered by concen- 

 trations of the color in which they are placed ; and the luminous 

 streak around the border appears to be even more distinctly devel- 

 oped in monochromatic than in white light. 



Having always entertained some doubts about the different refran- 

 gibilities of the colorific rays, notwithstanding the high philosophical 

 authority from which the theory emanated, I instituted a few obvious 

 experiments for the purpose of settling my mind on the subject. 

 Before stating them, I beg leave to make a few introductory remarks. 

 It is established that when the solar rays are transmitted through a 

 double convex lens, to a focal point, their convergency is caused by 

 the refraction which the rays undergo in the glass; and hence it ne- 

 cessarily follows that the distance of the focus from the lens is in- 

 versely as the degree of refrangibility possessed by the light. In 

 other words, if light were more "refrangible than it really is, its rays 

 would converge sooner to a focal point than they do, the same lens 

 being employed. Now according to the Newtonian doctrine, there 

 is a gradation of refrangibilities from the red to the violet rays ; the 

 rays of the latter being most refrangible, those of the former being 

 least so, and the colors included between these extremes, possessing 

 intermediate degrees of refrangibility. It naturally follows that when 

 the same double convex glass is used, the point of convergency or 

 focus will be nearest the lens in the violet rays, less near to it in the 

 indigo, still less so in the blue, and so on to the red rays, in which 

 the distance of the focus from the glass must be greatest, since they 

 possess less refrangibility than any of the other rays. Impressed 

 with these views, I obtained a double convex lens whose focal dis- 

 tance in the compound solar light was two feet, and mounted it on a 

 sliding stick, accurately graduated. Having decomposed, by a prism, 



* The bases formed by the saperior yellow rays and the inferior green, appear, 

 when viewed at a distance, to be larger than the rest, but this arises from their 

 greater illuminating power, by which they illustrate a space contiguous to them. 



