Eclipses. 23 



will then produce a partial eclipse, which would 

 be still greater if the moon were nearer her node, 

 as in the point H. In fine, if, in the moment 

 of the conjunction, the moon is precisely in her 

 node N, the eclipse will be central; for the centre 

 of the moon, if viewed from that of the earth, 

 will appear to coincide with the centre of the 

 sun. And if the apparent diameter AB (fig. 9) 

 of the sun S is greater than the apparent diameter 

 QR of the moon L, it will form round the moon 

 a ring, or a luminous crown ; and the eclipse is 

 then called annular. This ring of light will be 

 larger in proportion to the difference between 

 the apparent diameters of the sun and the moon. 

 But if the apparent diameter ON (fig. 10) of 

 the moon L is equally great or greater than the 

 apparent diameter BA of the sun S, he will ap- 

 pear entirely covered by the moon ; the eclipse 

 will then be total, and will endure so much 

 longer as the apparent diameter of the moon 

 shall exceed that of the sun. 



For an eclipse of the sun to be annular, the 

 case will be most favourable when the sun is in 

 perige, and the moon in apoge. And for an 

 eclipse to be total, the most favourable case is 

 when the sun is in apoge, and the moon in pe- 

 rige. 



The motion of the moon being swifter than 

 that of the earth, and the motion of both being 

 directed from west to east, that is, that of the 

 moon from Q to R (fig. 9), and from N to O 



