MATHEMATICAL PAPERS 16; 
preffion on the feat of vifion. Objects feen by reflection, as 
moft terreftrial bodies are, cannot be feen diftin&ly, unlefs they 
fubtend a certain angle.» The fame thing taking place in lu- 
minous obje&s, with a fmaller angle, when the thread of light 
becomes too (mall to be diftin&ly feen, the exterior limb of the 
planet will appear confuíed ; and every degree of confufion, 
arifing from a partial defe& of light, will operate upon the eye 
like a real diftortion of the obje&. If this opinion be right, 
as the diftance of centers is eafily calculated for any given mo- 
ment, perhaps the limits of vifion, as far as refpe&ts luminous 
objects, may be afcertained by accurate obfervations of this 
kind 
Cambridge, 27th December, 1782. | 
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