VII. An IMPROVEMENT of the Method of correcting the O B- 

 SERVED DISTANCE of the MOON from the S u N or a 

 FIXED STAR. By the Rev. Mr THOMAS ELLIOT^ Mini- 

 Jier of the Gofpel at Cavers. 



[Communicated by Mr RoBISON, General Secretary > Aug. 2. 1784.] 



PROBLEM. 



HAVING the apparent diftance of the Moon's centre from 

 a fixed Star, or from the centre of the Sun, together with 

 the apparent altitudes of their centres, to find the true diftance. 



SOLUTION. 



THE difference between the apparent and true altitudes, and 

 the angles which the Moon and Star make with the zenith and 

 each other, muft be known before the feveral corrections of di- 

 ftance are computed. 



THE difference between the apparent and true altitude of a 

 Star is the refraction in altitude, given p. 2. of Tables requi- 

 Jite to be ufed 'with the nautical ephemer is. If the diftance was taken 

 from the Sun in place of a Star, his refraction may be corrected 

 by fubtracting from it his parallax in altitude, given at the end 

 of the requifite tables, and the difference ufed inftead of the re- 

 fraction of a Star ', and, if great accuracy is required, the mean 

 refractions may be corrected by the barometer and thermome- 

 ter, according to Dr BRADLEY'S rule, p. 130. requifite tables. 



To find the difference between the apparent and true altitude 

 of the Moon, the horizontal parallax, given in the ephemeris 

 for the preceding noon or midnight, muft be reduced to the 

 time of obfervation, according to the inftructions in the requi- 



