C 5 6 5 ] 
between the Moon’s upper or lower limb, and that 
part of the limb from which the diftance .of the ftar 
is taken, I generally added the femidiameter of the 
Moon to, or fubtraded it from, the obferved altitude 
of the lower or upper limb, in order to have the ap- 
parent altitude of the center, and I found the apparent 
diftance of the ftar from the Moon’s center, by adding 
or fubtrading the Moon’s horizontal femidiameter, 
augmented according to her height, to or from the 
obferved diftance of the ftar from the Moon’s neareft 
or remoteft limb. 
This method will be exad enough, if the altitude 
of the Moon or ftar be not lefs than 5°. Having thus 
got three fides of the fpherical triangle formed by the 
Moon, the ftar, and the zenith 5 namely, the apparent 
zenith diftance of the Moon, the apparent zenith di- 
ftance of the ftar, and the diftance of the ftar from 
the Moon, I find the effed of refradion and parallax., 
in altering the apparent diftance of the ftar from the 
Moon, by the two following rules : 
Rule I. 
To find the effed of refradion in contrading the 
apparent diftance of two ftars, or of the Moon 
and a ftar. . 
Add together the logarithm-tangents of half the 
fum, and half the difference of the two zenith di- 
ftances, the fum abating 10 from the index is the 
tangent of arc the firft. To the logarithm-tangent 
juft found, add the logarithm-cotangent of half the 
diftance of the two ftars, the fum abating 10 from 
the index is the tangent of arc the fecond. Then 
