202 REMARKS ON THE SMALL PLANETS. 



to confirm the liypotliesis of Olbers. In its oppositions, this planet 

 comes sufficiently near the earth to attain the sixth degree of mag-ni- 

 tude and be visible to the naked eye, and owes its name to the white- 

 ness and purity of its light. 



III. 



Dating from the discovery of Vesta, the researches of astronomers 

 remained long unfruitful, although their attention was constantly 

 awake. It is true that Wartmann, at Geneva, in 1832, and Caccia- 

 tore, at Palermo, in 1835, gave notice of telescopic stars possessing 

 a distinct and quite rapid movement of their own ; but their observa- 

 tions, interrupted by unfavorable weather, were too incomplete and 

 uncertain to admit of their following' or again finding these assumed 

 planets ; nor was it till 1845, thirty-eight years after the discovery of 

 Vesta, that a postmaster named Ilencke, who occupied his leisure 

 moments with astronomy, perceived the fifth of these small planets, 

 and gave it the name of Astrea. Two years later he discoved Hebe, 

 and, dating from this epoch, the new asteroids have succeeded one 

 another so rapidly that their number at present is seventy [three.] 



It is not without some surprise that we see discoveries of this kind, 

 after having ceased for more than the third of a century, crowd upon 

 us in the course of late years. This astonishing success of cotem- 

 porary astronomy may be explained, in great measure, by the in- 

 crease in the number of observers, and by the construction of more 

 extensive and exact charts than those of which our predecessors 

 could avail themselves. The charts of Berlin, especially, which give 

 the stars of the first ten magnitudes in the ecliptic regions, have been 

 of the greatest service to astronomers in this kind of researches, while 

 the more recent charts of the observatory of Paris are already be- 

 coming of signal utility. It is very rarely that the discovery of an 

 asteroid can be regarded as the result of a lucky casualty. It is most 

 frequently only in the course of laborious watchings devoted to this 

 determined purpose, that a savant succeeds by means of a minute 

 and patient comparison of the different regions of the sky with the 

 charts which represent them, in detecting a disagreement, discover- 

 ing a star not catalogued, and verifying the existence of a proper 

 movement which shall assign a star to the class of planets. It may 

 be added that charts of the requisite completeness are as yet pro- 

 vided but for a small portion of the heavens, and the explorer who 

 would extend his search beyond this favored region must begin by 

 constructing a special chart of the tract which he proposes to survey. 



The ill success of Olbers in the ten last years of his researches is 

 attributable to the fact that his examination was not extended to stars 

 of less than the eighth magnitude. With not more than two or three 

 exceptions, the planets discovered within the last fifteen years 

 hardly transcend the ninth degree, while the greater part are of the 

 tenth, and some even below the twelfth degree of magnitude. It is 

 not easy therefore to estimate too highly the sagacity and admirable 

 patience of those volunteers in astronomy who. in the strength of 



