PHYSICAL ASTRONOMY. 559 



Driessen discovered a fifth of these planets, which \\as termed 

 In various quarters the chase was resumed with great ardor. In 1817 

 were found Hebe, Iris, and Flora; in 1848, Metis; in 1849, Hygaea; 

 in 1850, Parthenopc, Victoria, and Egeria; in 1851, Irene and Euno- 

 mia; in 1852, Psyche, Thetis, Melpomene, Fortuna, Massilia, Lutetia, 

 Calliope. To these we have now (at the close of 185C) to add nineteen 

 others ; making up the whole number of these Minor Planets at pres- 

 ent known to forty-two. 



As their enumeration will show, the ancient practice has been con- 

 tinued of giving to the Planets mythological names. And for a time, 

 till the numbers became too great, each of the Minor Planets was des- 

 ignated in astronomical books by some symbol appropriate to the 

 character of the mythological person ; as from ancient times Mars has 

 been denoted by a mark indicating a spear, and Venus by one repre- 

 senting a looking-glass. Thus, when a Minor Planet was discovered 

 at London in 1851, the year in which the peace of the world was, in 

 i manner, celebrated by the Great Exhibition of the Products of All 

 Nations, held at that metropolis, the name Irene was given to the new 

 star, as a memorial of the auspicious time of its discovery. And it 

 was agreed, for awhile, that its symbol should be a dove with an olive- 

 branch. But the vast multitude of the Minor Planets, as discovery 

 went on, made any mode of designation, except a numerical one, prac- 

 tically inconvenient. They are now denoted by a small circle inclos- 

 ing a figure in the order of their discovery. Thus, Ceres is (Q), Irene 

 is @, and Isis is @. 



The rapidity with which these discoveries were made was owing in 

 part to the formation of star-maps, in which all known fixed stars be- 

 ing represented, the existence of a new and movable star might be rec- 

 ognized by comparison of the sky with the map. These maps were 

 first constructed by astronomers of different countries at the suggestion 

 of the Academy of Berlin ; but they have since been greatly extend- 

 ed, and now include much smaller stars than were originally laid down. 



I will mention the number of planets discovered in each year. After 

 the start was once made, by Hencke's discovery of Astraea in 1845, 

 the same astronomer discovered Hebe in 1847 ; and in the same year 

 Mr. Hind, of London, discovered two others, Iris and Flora. The years 

 1848 and 1849 each supplied one; the year 1850, three ; 1851, two; 

 1852 was marked by the extraordinary discovery of eight new mem- 

 bers of the planetary system. The year 1853 supplied four; 1854, 

 six; 1855, four; and 1850 has already given us five. 



