Conditions of temperature to which the earth would he suhjected if it were compelled by a comet to descrihe the same orbit as the latter–The comets of Halley, and of 1680, examined from this point of view–Extremes of heat and cold: opinion of Arago : impossibility of living beings resisting such changes.

Arago has examined, in an indirect manner, the question of the habitability of comets; that is to say, he has considered how far the enormous distances through which a body passes in describing a very eccentric orbit around the sun, such as that of a cornetary orbit, are compatible with the existence of inhabitants similar to man. Could the earth, he enquires, ever become the satellite of a comet, and, if so, what would be the fate of its inhabitants?

Arago, basing his reasoning upon the comparative smallness of the masses of comets, regards the transformation of the earth into the satellite of a comet, as an event ‘ within the bounds of possibility, but which is very improbable, ’ an opinion no one at the present day will be inclined to dispute. He next supposes our earth successively made tributary to the comet of Halley and to that of 1680, and proceeds to consider the conditions of temperature to which our globe would be subjected whilst travelling in company with each.

With the comet of Halley our year would be sixty-five times longer than at present.