Their numbers are very great; several have been seen by the naked eye, and the telescope has increased the number to hundreds. What they are, or what purpose they fulfil in the economy of nature, is unknown. That they are material bodies of some sort, is known from their being attracted by other bodies near which they pass. A few of them are considered as permanent members of the system, as they return at certain periods to the sun, moving in very elliptic orbits, some of which are known. The comet which appeared in 1835, afforded all an opportunity of seeing it. The important point, relative to this, was that its orbit is known, and the interval between its periodical returns has been calculated. Comets of much greater magnitude and more splendid appearance have been seen, yet this, as it relates to astronomy, is the most important of all. The honor of first predicting its return belongs to Dr. Halley, a friend and contemporary of Sir Isaac Newton. What can be the use or nature of these bodies, is a question which naturally occurs, but to which science can yet give no satisfactory answer; their peculiarities being subjects of much greater wonder to the astronomer, than to the children who gaze on them. They are material bodies, it is true, yet composed of such materials as almost to leave one in doubt as to their deserving the name. The younger Herschel says that “the most unsubstantial clouds that float in the higher regions of the atmosphere, may be looked upon as dense and massive bodies, compared with the filmy and all but spiritual texture of a comet.” It is even probable that the substance is not to be compared for density with the air we breathe; that if a volume of cometary matter could be weighed, it would not be found so heavy as an equal volume of atmosphere.