SOLAR ECLIPSES, 

 of the latter, and produces the phenomenon called a solar 



5. When the globe of the earth intervenes between the moon 

 and the sun, it intercepts the light of the latter from a greater or 

 lesser part of the moon's disc, and produces the phenomenon 

 called a lunar eclipse. 



6. When a satellite of a planet passes into such a position that 

 the globe of the planet intervenes between the satellite and the 

 sun, the latter is eclipsed. 



7. When the disc of the moon or of a planet passes between 

 the eye of an observer and a fixed star, the star suddenly 

 disappears, and the phenomenon is called an occultation of the 

 star. 



8. When a planet passes between an observer and the sun's 

 disc there is seen projected upon the latter a small black circular 

 spot, and in virtue of the relative motion of the sun and planet 

 this black spot appears to pass across the disc of the sun from east 

 to west, producing the phenomenon called a transit of the planet. 

 Since at the period of a transit the planet must be between the 

 sun and the earth, and therefore nearer to the sun than the earth, 

 this phenomenon can only happen with an inferior planet. The 

 only planets, therefore, of which there can be transits are Yenus 

 and Mercury. 



SOLAR ECLIPSES. 



9. The discs of the sun and moon, though nearly equal, are 

 not exactly so, each being subject to a variation of magnitude 

 confined within certain narrow limits; and, in consequence, 

 the disc of the moon is sometimes a little greater, and some- 

 times a little less, than that of the sun. Their centres move 

 in two apparent circles on the firmament; that of the sun 

 in the ecliptic, and that of the moon in a circle inclined to the 

 ecliptic at a small angle of about 5. These circles intersect at 

 two opposite points of the firmament, called the moon's nodes. 

 In consequence of the very small obliquity of the moon's orbit to 

 the ecliptic, the distance between these paths, even at a consider- 

 able distance at either side of the node, is necessarily small. 

 Now, since the centres of the discs of the sun and moon must 

 ach of them pass once in each revolution through each node, it 

 will necessarily happen from time to time that they will be both 

 at the same moment either at the node itself, or at some points of 

 their respective paths so near it, that their apparent distance 

 asunder will be less than the sum of their apparent semi- 



M 2 163 



