128 OUTLINES OF NATURAL PHILOSOPHY. 



to the moon describes areas proportional to the 

 time. 



a The same may be also proved, from observations 

 of the Moon's parallax ; the Moon being near 

 enough to the earth to admit of her parallax being 

 accurately determined. 



b. The Moon's parallax, when least, is 53' 50".99, 

 and when greatest, 1 1' 22".99. Hence the 

 Moon's greatest distance is 6*'. 84 19 semidiameters 

 of the earth, and her least 55-9164. The mean 

 distance of the moon from the earth is therefore 

 59.8791, which is also the semi- transverse axis of 

 her orbit. 



c. A more accurate determination of these elements, 

 has fixed the mean equatorial parallax at 57' 11". 4; 

 the greatest distance of the moon at 1.05518, the 

 least at .94482, the mean distance being 1. 



Hence the eccentricity is .05518. 



In round numbers, the moon's mean distance is 60 



semidiameters of the earth ; and her diameter is 



to the diameter of the earth as 15' to 57' 11". 4, 



or as 3 to 11 nearly. VINCE, Astron. vol. i. 



171. 



. From the eccentricity of the moon's or 

 bit, the equation of the centre is found, 



