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 Observatory, 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 22° southwest of the sun, and appeared about as bright as a 42 magnitude star. Mr. Swift, who selected a position near Denver, Colorado, took with him his excellent comet-seeker for the special purpose of searching for intra-Mercurial planets. Two stars were seen by him at the estimated distance 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 Caneri. 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 indicated 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 revolution 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