There are few more interesting chapters in the history of astronomy than that which deals with the gradual introduction of meteors into an important position in the economy of the solar system. Regarded for a long time as simply atmospheric phenomena (though many ancient philosophers held another opinion), it has only been after a long and persistent series of researches that they have come at length to be regarded in their true light. But though the history of those researches is not only full of interest, but highly instructive and encouraging, this is not the place for entering at length into its details. I must present facts and conclusions, rather than the narrative of observations or calculations by which those facts and conclusions have been established. Nay, it would seem at first sight as though even the nature of meteors could have very little to do with the subject of this treatise, since we cannot suppose these small bodies to be inhabited worlds. It will be found, however, that, though this is certainly true, there are reasons for believing that meteors are associated in a very intimate manner with the general relations of the scheme of worlds forming the solar system.