( 1 71 ) 
Such fin allowance as this may perhaps be a 
proper Expedient to avoid accounting for Refrac- 
tion in coeleftial Obfervations, provided the Obiedsbe 
nearly parallel to the Horizon, or at a good height 
t b0V » f U n- F ° r ^ dlflances of are con traded 
Dy Keir action, when they are parallel to the Hori- 
zon, by the fame conftant quantity, be they high or 
low, that is by about one Second per Degree • the 
Chords of the Arches of the real and vifible diftances 
being always in the fame ratio as is the Sine of the 
Angle of Incidence to that of the refracted Angle. 
And this is the cafe wherein the RefraBion of the 
Air does lealt afFed the diftances of the Stars, which 
Diltances are ftill more and more contraded as they 
are nearer to a perpendicular Situation :So tliat a Dif- 
tance, for Example, of thirty Degrees lofes but half 
a Minute in a horizontal Site; but if the one Star be 
20 degrees high, and the other fifty, it will be lef- 
lened by above three times as much, or by i m 4I 
fee. If the one be 30 and the other 60 Degrees high, 
the fame diftance will appear lefs than 30 Degrees bv 
about one Minute ; the difference ftill decreeing as 
the Objeds are more elevated above the Honlon. 
But in all cafes to account for the effed of the Re 
fraction upon the Diftances of the Stars, requires be- 
tides fome Trigonometrical Work, the help of the 
afore-mentioned Table, which I herefubjoyn for the 
ufe of the Curious fuch as I long fince received it 
from its Great Author ; it having never yet, that I 
know of, been made publick# 
Tabula 
Bb 2 
