732 THE POPULAR SCIENCE MONTHLY. 



to us the whole of living Nature, each varied offshoot fitly joined to- 

 gether, sloping gently back along the vast converging lines of ordinary 

 generation to one grand starting-point, wherein till the fullness of time 

 every living thing, from the microscopic diatom to the giant sequoia, 

 and from the shapeless amoeba to the stateliest of bipeds 



" Lay hidden, as the music of the moon 

 Sleeps in the plain eggs of the nightingale." 



Belgravia. 



-- 



THE PLANET VULCAN. 



By Professor DANIEL KIEKWOOD. 



THE discovery of an intra-Mercurial planet during the total eclipse 

 of July 29, 1878, has given new importance to any previous 

 speculations on the question of its existence. A brief historical re- 

 view of the subject will not be without interest. 



In an article by the writer, " On the Probable Existence of Undis- 

 covered Planets," written immediately after the discovery of Neptune, 

 and published in the Literary Record and Journal of the Linncean 

 Association of Pennsylvania College, 1 the question was thus consid- 

 ered : 



" The distance from the centre of Jupiter to the nearest satellite is about 

 three times the equatorial diameter of the primary. If, therefore, we suppose 

 the distance of the nearest primary planet to have the same ratio to the diam- 

 eter of the sun, the orbit of such planet will be somewhat less than 3,000,000 

 miles from the sun's centre. Consequently, in the interval of 37,000,000 miles 

 there may be four planets, the orbit of the nearest having the dimensions above 

 stated, and their respective distances increasing in the ratio of Mercury's dis- 

 tance to that of Venus. Such bodies, however, in consequence of their near- 

 ness to the sun, could hardly be detected except in transiting the solar disk." 



It is well known that the disturbing influence of the other planets 

 causes an advance in the position of Mercury's perihelion. In a cen- 

 tury this change amounts to 10' 43," which, according to Leverrier, is 

 38" more than can be accounted for by the influence of the known 

 planets. This great astronomer inferred, therefore, that a planet, or 

 possibly a zone of extremely small asteroids, must exist within the 

 orbit of Mercury. 



The conclusions of Leverrier were communicated to the French 

 Academy in the autumn of 1859. Soon after their publication Dr. 

 Lescarbault, an amateur astronomer as well as a medical practitioner 

 of Orgeres, some forty miles southwest of Paris, announced that, on 

 March 26, 1859, he had observed the passage of a dark circular spot across 



^ol. iii., April, 1S47, p. 131. 



