ASTRONOMY. 



ther the sun or the earth is placed, has been called the 

 Perigee ; supposing that it is the point where the sun 

 in motion approaches nearest to the earth at rest. 

 On the contrary supposition, it would be called the Pe- 

 rihelion. The same applies to the terms Apogee and 

 Aphelion. 



It must be observed, that the distances of the Sun 

 and Earth, now treated of, are only the relative 

 distances, referred to an imaginary standard, and 

 not compared with any known magnitude, such 

 as the diameter of the earth. The observations on 

 which such a comparison as this must be founded, 

 and by which the sun's parallax is ascertained, 

 cannot be explained till the planetary system is 

 understood. In the mean time, it may be re- 

 marked, that even by help of the observations 

 above described, it may be inferred, that the sun's 

 parallax is less than 10". 



From observations of the sun's solstitial altitudes, 

 we saw, 87., how the latitude may be deduced. 

 In order to make the deduction with accuracy, the 

 sun's altitudes must be corrected for the parallax; 

 and it may be easily shewn, that if the horizontal 

 parallax of the sun is so great as 10", the lat. of 

 Greenwich, for example, determined without ma- 

 king the due allowance for it, would be erroneous, 

 by 1". The latitude determined by observations of 

 the stars, is free from this error, and therefore 

 ought not to agree with the former by 7". Now, 

 the correction necessary to be made, in order that 

 the deterniinatipn deituced from the altitude of the 



sun* 



