382 ANNUAL OF SCIENTIFIC DISCOVERY. 



and it is this vegetation which makes the sterile par's of the moon appear 

 as bright luminous streaks. According to M. Schwabe, these lines of vege- 

 tation are more par;k"ularly visible in the very bright parts of the moon, 

 whirh are circumscribed by a number of particularly prominent mountain 



peaks. 



LEVEREIEirS NEW PLANET "VULCAN." 



On the 2d of January, 1830, M. LeVerner communicated to the Academy 

 of Sciences a remarkable paper on the theory of Mercury. In studying the 

 twenty-one transits of that body over the sun between 1097 and 1848, he 

 found that the observations could not be represented by the received ele- 

 ments of the planet, but that they could be all represented, nearly to a 

 second, by augmenting by thirty-eight seconds the secular motion of the 

 perihelion of Mercury. In order to justify such an increase we must in- 

 crease the mass attributed to Venus one-tenth at least of its value, which, 

 from sixty years' meridian observations, has been found to be the four 

 hundred thousandth part of that of the sun. If we admit this increased 

 mass of Venus, we must conclude, either that the secular variation of the 

 obliquity of the ecliptic, deduced from observations, is affected with errors 

 by no means probable, or that the obliquity is changed by other causes 

 wholly unknown to us. If, on the other hand, we regard the variation of 

 the obliquity of the ecliptic, and the causes which produce it, as well estab- 

 lished, we must believe that the excess of motion in the perihelion of Mercury 

 is due to some unknown action. 



" I do not intend," sa.ys M. LcVcrrier, "to decide absolutely between these 

 two hypotheses. I wish only to draw the attention of astronomers to a grave 

 difficulty, and to make it the subject of a serious discussion." We must, 

 therefore, as he suggests, find a cause which shall impress upon the perihe- 

 lion of Mercury these thirty-eight seconds of secular motion, without pro- 

 ducing any other sensible effect upon the planetary system. 



M. LeVerrier then shows that a planet between Mercury and the sun, the 

 size of Mercury, situated at half his mean distance from the sun, if moving 

 in a circular orbit slightly inclined to that of Mercury, would produce the 

 thirty-eight seconds of secular motion in his perihelion. But when he con- 

 siders that such a planet would have certainly a very great brightness, he 

 cannot think that it would be invisible at its greatest elongation, or during 

 total eclipses of the sun. 



"All these difficulties," he adds, " disappear, if we admit, in place of a 

 single planet, small bodies circulating between Mercury and the sun; " and 

 he thinks their existence not at all improbable, seeing that we have already 

 a ring of fifty-eight such bodies between Mars and Jupiter. 



A short time subsequent to the publication of this paper, M. LeVerrier 

 received a communication from a physician in very humble circumstances, 

 in the little town ofOrgercs,in France, M. Lescarbault, stating that he 

 had " actually discovered an intra-Mcrcurial planet making a transit across 

 the disk of the sun." 



The circumstances of the case were briefly as follows : 



M. Lescarbault, who had studied astronomy solely from a love of the 

 science, conceived the idea, as far back as 1845, of observing systematically 

 the sun, with a view of seeing whether any planet other than Venus or 

 Mercury could be detected in making transit across the solar disk. He 



