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supposed to be found. During the eclipse of 1878, Professor Watson, of Ann Arbor, and Professor Lewis Swift, both able and experienced observers, thought that they had detected some such bodies. But critical examination left no doubt that what Watson saw was a pair of fixed stars which had always been in that place. How it was with the observations of Professor Swift has never been certainly ascertained, because he was not able to lay down the position with such certainty that positive conclusions could be drawn.

Notwithstanding such failures, observers have repeated the search during several of the principal total eclipses. The writer did so during the eclipse of 1869, and again during that of 1878, the search being made with a small telescope. In recent times the powerful agency of photography has been invoked by Professors Pickering and Campbell during the eclipses of 1900 and 1901. Campbell's results during the latter eclipse were the most decisive yet reached. With his photographic telescope some fifty stars were photographed, some as faint as the eighth magnitude, but they were all found to be known objects. It therefore seems certain that there can be no intramercurial much brighter than the eighth magnitude. It would take hundreds of thousands of such planets as this to produce the observed motion of Mercury. So great a number of these bodies would produce a far brighter illumination of the sky than any that we see. The result therefore seems to be conclusive against the view that the motion of the perihelion of Mercury can be produced by intramercurial planets. In addition to all these difficul-