Orbits described by bodies under the action of a central force are always conic sections, as Sir Isaac Newton proved. There are two classes of such curves: those which return into themselves, such as the circle and ellipse, and those which do not, the hyperbolæ. If a body travel in the first or closed class about the Sun, it is clearly a member of his family; if in the second, it is a visitor who bows to him only in passing and never returns. Which orbit it shall pursue depends at a given distance solely upon the speed of the body; if that speed be one the Sun can control, the body will move in an ellipse; if greater, in an hyperbola. Obviously the Sun can control just the speed he can impart. Now a comet entering the system from without would already possess a motion of its own which, when compounded with the solar-acquired speed, would make one greater than the Sun could master. Comets, therefore, if visitors from space, should all move in hyperbolæ. None for certain do; and only six out of four hundred even hint at it. Comets, then, are all members of the solar family, excentric ones, but not to be denied recognition of kinship for such behavior. Still, admittance to the solar family circle was denied to meteorites and shooting-stars. Thus Professor Kirkwood, in 1861, had considered “that the motions of some luminous meteors (or cometoids, as perhaps they might be called) have been decidedly indicative of an origin beyond the limits of the solar system.” Here cometoid was an apt coinage, but when comets were later shown not to be of extra-solar origin, the reasoning carried luminous meteors in its train.[1] Finally Schiaparelli, in 1871, concluded an able Memoir on the subject with the decision that “a stellar origin for meteorites was the most likely and that meteorites were identifiable with shooting-stars.”[2] A pregnant remark this, though not exactly as the author thought, for instead of proving both interstellar, as he intended, both have proved to be solar bound. [1] “Mem. del Reale Inst. Lombardo,” Vol. XII. III della serie III. [2] Quoted in “Luminous Meteors,” Committee’s Report for 1870-1871, p. 48. It was Professor Newton, in 1889, who first showed that meteorites were pursuing, as a rule, small elliptic orbits about the Sun, and that their motion was direct. He, too, was the first to surmise that meteorites are but bigger shooting-stars.