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emergent pencil will be found to make with a per- 
pendicular to the terminating furface an angle of 
49° 6'4 -j and will be inclined to the firft incident 
pencil in an angle of 14 degrees, 28 minutes, 20 fe- 
conds. Nor is there any other plane belides this 
which will thus unite the rays. If planes parallel 
to it cut the rays any where but in their point of con- 
vergence, they will be parallel to each other, but ex- 
hibiting their feveral colours. And planes not pa- 
rallel to it, will every where give a coloured image, 
excepting only when they pafs through the point of 
convergence; but then the rays having crofs’d at 
at thatpoint, will thenceforth diverge from one an- 
other, and give a coloured lpedrum. 
From all which it appears that light refraded thro’ 
different media may emerge colourlefs, although its 
firft direction be confiderably altered. And that its 
mean diredion may remain the fame, though its.ex- 
tremities be fenfibly tinged with colours. Pofitions 
which, I know not by what mifhap, have been deem- 
ed paradoxes in Sir Ifaac Newton’s theory of light , 
but which are really the neceffary confequences of it. 
Of Telef copied Objett-GlaJJes giving an Image free 
from Colours . Fig. 8 and 9. 
If the extreme rays, the red and violet, after one 
or more refradions, diverge from points D and d , 
the diftance of the point of divergence of the leaft 
refrangible from the lens, being greater than that of 
the moft refrangible, fuch a femidiameter of the laft 
fpherical furface, from which they are to pafs into 
