them, (4) shows that certain of them are its necessary consequences, would probably be right, even though it had not been yet shown that among all other possible theories there is not one which is not directly contradicted by some known facts. As, however, the general theory of the ejection of all cometic and meteoric bodies from orbs—suns of all orders, giant planets, terrestrial planets, planetoids, and moons—is as strongly supported by such negative evidence as it is by direct positive evidence, I venture to say that a case not easily shaken has been made out in its favor. No one, so far as I know, has yet indicated any objection against the theory in the generalized form in which alone I have ever advanced it. Objections have been urged against it in the form in which it has been supposed that I have maintained it. It has been very clearly shown that meteors can not come to the earth from the sun unless they strike the earth on their first course out from the central orb; it has been proved that a considerable proportion of the meteoric and cometic systems known can not have had their origin either in our sun or in any of his fellow-suns, the stars; it has been urged as effectively that the giant planets can not eject comets or meteors; and it has been shown clearly that our earth can not, in any stage of which geology has traced the records, have ejected bodies which could thenceforth travel in interplanetary space as meteors or meteor-flights. But, in these objections against specific theories of the possible origin of comets and meteors, we may find some of the strongest, if not the very strongest, arguments for that general theory to which each specific theory points, so soon as we notice that the arguments supporting each specific theory are such as decline to be limited to that theory alone.
In fine, as I suggested at the outset, if we apply to the several specific theories of comets and meteors the general principles laid down by Professor Newton, we find ourselves led irresistibly to that general theory which I have sketched above, and presented with more elaboration of detail elsewhere.
THE masses of snow and ice known as glaciers, which are found upon high mountains, have been the object of many studies; and it is a matter to be wondered at that the same has not been the case with the immense beds of snow that every winter cover parts of Europe, Asia, and America, to disappear in the following spring. It has perhaps been thought that the latter have less influence upon climate in general than upon other more special phenomena. But the observations that follow will tend to show that this influence exists and the subject is one well worthy to be studied.