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42 with the data, but the merit of the solution is all his own. The Astronomer-Royal has, as it were, dug up from some Assyrian mound, a tablet with mystic cuneiform characters, and M. Hansen has supplied the key to the interpretation. The moon is so eagerly scrutinised at Greenwich, that any deviation from the prescribed path is soon detected. M. Hansen had already, on more than one occasion, vindicated the law of gravitation, by reducing unexplained lunar irregularities to its dominion. When again applied to, he set to work to discover the cause of the irregularity. The deviation was slight, but if the moon does not keep time to a very second, some explanation is required; and, on this, as on all former occasions, M. Hansen was triumphant. He has given a most marvellous solution, but one in which all astronomers have acquiesced.

The scientific statement of the solution is, that the moon's centre of gravity and her centre of figure are not coincident, the one being distant about 37 miles from the other. Most momentous results flow from this. The one hemisphere must be lighter than the other. This, indeed, is but another way of stating the discovery. The sphere of the moon may be regarded as made up of a light half and a heavy one—the lighter being always turned towards the earth.

But how could such a strange discovery be made? It would not be easy to give a popular explanation of