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 or conceivable by us, can ever reproduce what the heavens must have been like at periods of millions of years ago. There could be no more interesting sight than a glimpse at the starry heavens in the time of the ichthyosaurus. We have read somewhere of a fable to the effect that the last object on which an eye rested ere it closed imprinted its picture permanently on the retina. Would that such a notion were founded on fact, and that the impression of the last celestial picture on which the eye of the ichthyosaurus gazed before he breathed his last were treasured up in the fossilized organism.

In the consideration of the gradual transformation of the heavens, I have found it convenient to speak as if the earth, or rather the solar system to which the earth belongs, occupied a fixed position in space. But when we have learned that some or all of the stars are in movement, it seems right to inquire whether the sun might not also participate in the motion. May not the sun be engaged in some mighty voyage through the celestial spaces, taking in its company the earth and the other planetary bodies by which it is attended? Here is, indeed, a grand problem; I propose to enter into its discussion with the assistance of certain recent investigations.

In the first place, it must be remembered that for the sun to be actually devoid of movement could be little short of miraculous. There are, of course, an infinite number of different movements possible, for there is every degree of velocity and difference of direction to be considered. On the other hand there is only one type of rest, or absolute quiescence, and it would be just as likely that a body should possess any stated velocity, say ten miles, ten