C 758 ] 
light by the water was equal to that by the glafs ; 
that is, till the objed, tho’ confiderably refraded, 
by the excefs of the refradio.n of the water, appeared 
neverthelefs quite free from any colours proceeding 
from the different refrangibility of light ; and, as 
near as I could then meafure, the refradion by the 
water was about { of that by the glafs. Indeed I 
was not very exad in taking the meafures, becaufe 
my bufinefs was not at that time about the propor*- 
tions, fo much as to fhew, that the divergency of 
the colours, by different fubffances, was by no means 
in proportion to the refradions ; and that there was 
a poffibility of refradion without any divergency o£ 
the light at all. 
. Having, about the beginning of the year 1757, 
ta-ied thefe experiments, I foon after fet about grind- 
ing telefcopic objed-glaffes upon the new principles 
of refradions, which I had gathered from them ; 
which objed-glaffes were compounded of two fphe- 
rical glaffes with water between them. Thefe glaffes 
I had the fatisfadion to find, as I had expeded, free 
from the errors arifing from the different refrangi- 
bility of light : for the refradions, by which the 
rays were brought to a focus, were every-where the 
differences between two contrary refradions, in the 
fame manner, and in the fame proportions, as in the 
experiment with the wedges. 
? However, the images formed at the foci of thefe 
objed-glaffes were ftill very far from being fo di- 
ffindt as might have been expeded from the removal 
of fo great a difturbance ; and yet it was not very 
difficult to guels at the reafon, when I considered, 
that the radii of the fphericaj furfaces of thofe glafles 
were 
