The Earth was not their birthplace. It is alien ground in which they lie at last and from which we transfer them to glass cases in our museums. This fact about their parentage they tell by the speed with which they enter our air. They become visible 100 miles up and explode at from 20 to 10, and their speed has been found to be from 10 to 40 miles a second, which is that of cosmic bodies moving in large elliptic orbits about the Sun,—a speed greater than the Earth could ever have imparted. Four classes of such small celestial bodies tenant space where the planets move: sporadic shooting-stars, meteorites, meteor-streams, and comets. The discovery of the relation of each of these to the solar system and then to each other forms one of the latest chapters of astronomic history. For they turn out to be generically one. It was long, however, before this was perceived. The first step was taken simultaneously by Professor Olmstead of Yale and Twining in 1833 from reasoning on the superb November meteor-shower of that year. All the shooting-stars, “thick as snowflakes in a storm,” had a common radiant from which they seemed to come. Thus they argued that the meteors must all be travelling in parallel lines along an orbit which the previous shower, of 1799, showed to be periodic. This was the first recognition of a meteor-swarm. The next advance was when Schiaparelli, in 1862, pointed out the remarkable connection between meteor-swarms and comets. On calculation the August meteor-stream and the comet of 1862 proved to be pursuing exactly the same path. Soon other instances of like association were discovered, and we now know mathematically that meteor-streams can be, deductively that they must be, and observationally that they are, disintegrated comets. More than one comet has even been seen to split. Then came the recognition that comets are not visitors from space, as Sir Isaac Newton and Laplace supposed, but part and parcel of our own solar system. Without going into the history of the subject, which includes Gauss, Schiaparelli, and finally Fabry’s great Memoir, much too little known, the proof can, I think, be made comprehensible without too much technique, thanks to the fact that the Sun is speeding through space at the rate of eleven miles a second.