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of the Sine of the Angle of Incidence to that of the 
Refraded Angle, encreafing as the Beam approaches, 
makes a very notable difference in the place of an. 
Objed near the Horizon : but in. Obj.eds that are 
much elevated, the Refradions become fmall,and their 
Differences fcarce exceed a Second per Degree j fo 
that they are fufficientiy the fame, as if the Incident 
and Refraded Angles were on the Surface of a Sphere 
of Air of the fame uniform Denfity clofe ad- 
jpyning to the Eye. 
When therefore the Stars are twenty degrees or 
upwards elevated above the Horizon, we may take it 
for granted, without fenfible Error, that the Sines 
of the true and apparent Diftances from the Vertex, 
are in the fame conflant ratio. Hence it will ap- 
pear that the Diftances of all the Stars are feen lefs 
than they really are, in whatever pofition they are 
taken, and that not lefs than a Second per Degree of 
the diftance \ that is, a diflance of 30 degrees, for 
example, is contraded at leaft fo many feconds, and 
one of 60. gr. no lefs than a Minute, if the diftances 
be taken by an inftrument that is truly divided*. 
So that when Mr. Hevelius , to ffiew the exadnefs of 
his Obfervations, brings eight Diftances, as taken by 
his Sextant, which exadly com pleat the Circle, both, 
in Longitude and Right Afcenfion j the confequence- 
is really quite oppofite to his Defign : for if thofe 
diftances were the true ones, they being all con- 
traded by appearing through a refrading Medium, 
the Sum of the eight differences of both Longitude 
and Right Afcenfion, ought to fall fhort of a whole 
Circle or 360 degrees by at leaft fix minutes } fo that 
I am inclined to believe that the fixty degrees of 
Mr. Hevelius's Sextant wanted about a Minute of its 
tmie quantity... §uch; 
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