ns 
ft 
; 
; 
a as 
nes 9 
—— 
i 
REFRANGIBILITY of LIGHT. t9 
conftruction and a fimple lens, if they had been attentively ob- 
ferved, would have led Dr Hoox to the truth; and a man of 
his zeal and invention would not have failed to apply the dif- 
covery to the improvement of optics, not to mention the tri- 
umph it would have afforded the opponent and rival of New- 
TON, to have aflerted, and had it in his power to make good 
his affertion, that. in fome cafes the violet rays are the leaft re- 
frangible, and the red rays the moft refrangible. 
Even Mr Dottonp could not conceive that the prifmatic 
colour could be corrected by refractions which are .all made 
the fame way; and. ftill lefs would he have admitted that fin- 
gle refractions may take place without divergency or colour *.. 
As this continues to be the opinion of the beft informed opti- 
cians of the prefent day, it will be neceffary to enter into a more 
explicit inveftigation of the fubject. 
Fic. 2. Let ABC reprefent a glafs prifm, and BCD a 
prifm of water in contact with it; and let the angles of thefe 
-  prifims be fo proportioned to each other, that a ray of light S I, 
which enters the glafs prifm perpendicularly, fhall,, after being 
refracted from the perpendicular at the point G, in pafling out 
of the glafs into the water, emerge at K, perpendicular to the 
fide C D of the water prifm, which is fuppofed to be confined. by 
parallel plates of glafs. As the ray both enters and emerges 
from the refracting mediums perpendicularly, it will fuffer no 
refraction, excepting when it pafles from the glafs into the wa- 
ter, where its incidence is oblique. Here it, will be ‘refracted 
_ from the perpendicular, and, will emerge coloured, the violet 
rays being moft refracted, and the red rays leaft refradted. . ., 
Let the water be now impregnated with antimony or mer- 
cury, to increafe its difperfive power. As this will alfo increafe 
its mean refraétive denfity, and occafion a diminution of the 
C2 refraction 
_.* Philofophical Tranfations of London, vol. 1. page 74¢. 
