734 THE POPULAR SCIENCE MONTHLY. 



But the astronomer of Brazil did not stop with denying the truth of 

 Lescarbault's observations. He boldly called in question the conclusion 

 derived by Leverrier himself from a laborious discussion of the observed 

 transits of Mercury. It now appears, however, that in this case also 

 his position was most unfortunately taken. 



It has been frequently said that if an intra-Mercurial planet exist, 

 of any considerable magnitude, it ought to be visible during total 

 eclipses of the sun. But who has not remarked the difficulty of finding 

 a small or faint object when we know not where to look for it, and how 

 easily it may be found when its position has been once pointed out ? 

 Mitchel's detection of the companion of Antares and Clark's discovery 

 of that of Sirius are cases in point. Fortunately, however, neither 

 argument nor explanation is any longer necessary. The new planet 

 was undoubtedly seen during the total eclipse of July 29, 1878, by two 

 astronomers, Prof. James C. "Watson, director of the Ann Arbor Obser- 

 vatory, and Mr. Lewis Swift, of Rochester, New York. The former is 

 the discoverer of more than twenty asteroids ; the latter is an amateur, 

 who has detected several new comets. Prof. "Watson was stationed at 

 Separation, Wyoming Territory. The planet was not found by him till 

 half the time of totality was past. It was about 2^ southwest of the 

 sun, and appeared about as bright as a 4|- magnitude star. Mr. Swift, 

 who selected a position near Denver, Colorado, took with him his ex- 

 cellent comet-seeker for the special purpose of searching for intra- 

 Mercurial planets. Two stars were seen by him at the estimated dis- 

 tance of 3 southwest of the sun. They were of the same magnitude 

 about the fifth and at a distance apart of six or seven minutes. A 

 straight line drawn through them pointed very nearly to the sun's 

 centre. Mr. Swift supposed one of the stars to be Theta Cancri. The 

 other was doubtless the planet observed by Prof. Watson, although 

 the estimated distance from the sun was somewhat greater. Both 

 observers describe it as a red star. According to Prof. Watson, " it 

 shone with an intensely ruddy light, and it certainly had a disk larger 

 than the spurious disk of a star." Its appearance in the telescope indi- 

 cated that it was approaching its superior conjunction, or, in other 

 words, was situated beyond the sun. 



The distance of Vulcan from the centre of the system, though still 

 uncertain, is supposed to be about one-seventh that of the earth. If 

 this estimate be nearly correct, the solar light and heat at its surface 

 must be about fifty times greater than at the surface of the earth. The 

 corresponding period is nearly twenty days. In other words, Vulcan's 

 year is believed to be less than three weeks in length. The sun' is 

 twenty-five days in completing its axial rotation ; so that in the new 

 planet we have probably another instance in which, as in the case of 

 the inner satellite of Mars, a planetary body performs its orbital revo- 

 lution in less time than is occupied by the central orb in completing 

 its rotation. Again, as seen from the sun's surface, all the old planets 



