76 On th UNEQUAL, &c. 
which it is for the red and violet rays. Thefe three orders of 
rays will therefore fuffer an equal refraction, being each of 
them attracted towards the glafs with the force two; and when 
this is the cafe, it appears from the obfervations, that the inde- 
finite variety of rays of intermediate colours and fhades of co- 
lours, which altogether compofe folar light, will alfo be regu- 
larly bent from their re¢tilinear courfe, conftituting what has 
been termed aplanatic refraction. 
- Tuese cafes of attraction might be farther illuftrated by 
means of diagrams. But after the explanation already given 
of the fecond, third, fourth, fifth, fixth, feventh and eighth fi- 
gures, this would be unneceflary. And it need f{carcely here be 
obferved, that the above rough ftatements in round numbers, 
are intended to give a clear idea of the nature of the various 
cafes of unequal refrangibility, and not to afcertain its quantity 
in any particular cafe. A full inveftigation of the fubject, and 
an account of fome digreflions lefs immediately conneéted 
with the principal object which occurred in the courfe of the 
enquiry, could not be brought within the compafs of the pre- 
fent communication. 
HI, 
