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 tens of millions of years, I do not know of any facts by which he could be contradicted. The longer the time the more complete would have been the transformation in the visible objects on the sky.

Except that the stars of this remote antiquity must have been totally different from our present stars, we know but little of them. Indeed, I might almost say we can know nothing. Possibly some of our telescopic nebulae and clusters, whose distances are believed in many cases to be greatly in excess of the average distance of the stars, might not have been so totally transformed by their proper motion even in millions of years as to be unrecognisable by an eye familiar with the appearance they bear at present. There can, however, be no doubt that greatly as the stars may have changed the aspect they present to the terrestrial inhabitants, the sun, to which in the same time those inhabitants owe so much can have undergone but little appreciable alteration. The luxuriant vegetation of the coal measures demonstrates that the great luminary must have dispensed light as well as heat in those ancient days. The same fact is strikingly exemplified by the presence of eyes in extinct animals. Indeed, in some cases the eyes of creatures now only known to us by their fossil remains, seem to have been of the most elaborate character. Who that has ever visited any of our geological museums has not been interested in examining the great eye of the ichthyosaurus? In that unique organ of vision there is a remarkable apparatus of bony plates, apparently intended for adaptation of the organ to varying conditions. It is obvious that for some reason or other, as to which we can only speculate, a visual organ of excessive power and adaptability was required for this wondrous fish-reptile. I