by their motion, leave their trace in the form of elongated trails or streaks, thus betraying themselves at once on the photographs. In this way Charlois, of Nice, Italy, has found nearly ninety small planets. All these planetoids, as the minor planets are often termed, are quite small, being but twenty to one hundred miles in diameter, and not consequential members of the solar system. Bode’s law thus fulfilled its temporary mission; but egregiously failed when Neptune claimed admission to a place in the solar system, for its distance from the sun was utterly out of harmony with that required by the law of Bode. III. HOW NEPTUNE WAS FOUND. The patience of Job had a strong parallel in the labors of those tireless toilers to whose minute computations we owe our knowledge of Neptune’s path in the skies. For this far-off planet was discovered not by the use of a telescope, or any optical instrument, but simply by a process of mathematical reasoning. The story is simply this. For sixty years after Uranus was recognized, there were irregularities in its motion that could not be satisfactorily accounted for. In the orbit that it was believed to pursue, it was sometimes in advance of its proper position, and sometimes it seemed to fall behind. Sometimes it appeared to be drawn a little to the right, and at other times as far the other way. The thought at last came separately to several penetrating minds, not that the observations of its position were in error, but that Uranus must be drawn away from its supposed path by the attraction exercised upon it by some unseen body. And if such an object existed, was it a planet? Where was it? How large was it? What was its path in the far-off ether? [Illustration: THE MOVEMENT OF URANUS AND NEPTUNE. The inner circle shows the position of Uranus at various dates; the outer circle the position of Neptune. The arrows show the direction toward which Uranus was drawn.]