the sun's disk, which he thought might have been the transit of an intra Mercurial planet. He stated further that he had delayed the publication of the fact in the hope of obtaining confirmatory observations. On the appearance of this statement Leverrier at once determined to seek an interview with the observer, in order to test the truth of his discovery. With the details of this interview the public is familiar. After a thorough examination of Lescarbault's original memoranda, as well as of his instruments and methods of observation, Leverrier was satisfied that the amateur astronomer of Orgères had really observed the transit of an intra-Mercurial planet. From the notes furnished by Lescarbault, the director of the Paris Observatory estimated the period of the planet at nineteen days seventeen hours; its mean distance from the sun, 13,000,000 miles; the inclination of its orbit, 12° 10'; and the greatest elongation of the body from the sun, 8°. The apparent magnitude of the solar disk, as seen from Vulcan's estimated distance, is fifty times greater than as seen from the earth.
The sun was again watched during the last days of March in 1860 and 1861, in the hope of reobserving the new member of the system. The search, however, was unsuccessful until March 20, 1862, when Mr. Lummis, of Manchester, England, between eight and nine o'clock a. m., observed a perfectly round spot moving across the sun. Having satisfied himself of the spot's rapid motion, he called a friend, who also noticed its planetary appearance. From these imperfect observations two French astronomers, MM. Valz and Radau, computed elements of the planet: the former assigning it a period of seventeen days thirteen hours; the latter, one of nineteen days twenty-two hours. From 1862 to 1878 the planet was not seen, or at least no observation was well authenticated. The transit of Mercury, however, on May 6, 1878, afforded new evidence of the truth of Leverrier's theory that Mercury's motion is disturbed either by a planet or a zone of planetary matter within his orbit.
We must now refer to a very unpleasant incident in the history of this interesting discovery. This is nothing less than the charge, by an eminent astronomer, that the observations and measurements claimed by Dr. Lescarbault were a pure fabrication. M. Liais, a French astronomer employed at Rio Janeiro by the Brazilian Government, claimed to have been engaged in an examination of the sun's surface with a telescope of twice the power of Dr. Lescarbault's, at the very time of the latter's alleged discovery of the planet. M. Liais says, therefore, that "he is in a condition to deny, in the most positive manner, the passage of a planet over the sun at the time indicated." The weight of this negative testimony has, perhaps, been over-estimated; and Lescarbault, who for eighteen years has quietly submitted to the charge of falsehood and dishonesty, may perhaps yet retort that, if M. Liais was examining the sun at the time referred to, his merit as an observer cannot be highly rated.