ASTRONOMY. 247 



eclipse takes place, such as that of the 15th May, 1836, when a ray of 

 light appears around the disk of the moon. This is ia consequence of the 

 apparent diameter of the moon being less than that of the sun ; at other 

 times it is greater, and then a total eclipse takes place. 



" The moon is eclipsed whenever the earth comes between it and the 

 sun: in consequence of which it is deprived of the light of that luminary. 

 As the moon revolves round the earth once in every twenty-eight days, 

 it might at first be supposed that an eclipse would take place once in 

 every month, as the moon must during that period pass between the 

 earth and the sun. This would be the case, only the moon does not pas* 

 in an exact line between the earth and the sun : the inclination of the 

 orbit of the moon to the plane of the eliptic prevents this occurrence taking 

 place so often ; but whenever the moon passes the earth in an exact 

 line with the sun, that is, whenever the three bodies are in an exact line 

 with each other, the moon is eclipsed. 



" Every eighteen years and ten or eleven days the order in which 

 eclipses occur, is the same as that of the previous eighteen years. It might 

 therefore be imagined that a correct list of eclipses for eighteen years 

 would be sufficient for all purposes ; as by adding the eliptic period as 

 many times as required, the period of an eclipse might be known at 

 any distance of time. This would be correct if every eclipse appeared 

 under precisely the same circumstance as its corresponding eclipse in the 

 preceding or following period ; but this is not the case. An eclipse of 

 the moon, which, in the year 565, for example, was of six digits, was in 

 the year 583 of seven digits, and in 901 nearly eight. In 908 the eclipse 

 became total, and it remained so for about twelve periods, or until the 

 year 1088 ; this eclipse continued to diminish until the commencement of 

 the fifteenth century, when it totally disappeared in the year 1413. In 

 like manner an eclipse of the sun, which first appeared at the North 

 Pole in June 1295. proceeded more southerly at each period. On the 

 7th August, 1367, it made its first appearance in the north of Europe; 

 in 1439 it was visible all over Europe ; in 1601, which was its nineteenth 

 appearance, it was central in London ; in 1818, on the 5th of May, it was 

 visible in London, and was again central nearly in the same place on the 

 16th of May, 1836. At its thirty-ninth appearance, August 10th, 1980, 

 the moon's shadow will have passed the equator, and as the eclipse will 

 take place nearly at midnight, it will be invisible in Europe, Africa, and 

 Asia. At every subsequent period the eclipse will go more and more 

 towards the south, until, finally, on the 30th September, 2665, which 



