DISTANCE, SIZE, AND MASS.

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Roughly, we may take the moon’s diameter as two-sevenths of the earth’s, her surface as two twenty-sevenths, her volume as two ninety-ninths. Of theseproportions, the most interesting is that between themoon’s surface and the earth’s ; for neither the dia-meter nor the volume of the moon is speciallyrelated to her condition as a globe comparable withour earth as respects those features which affect ourown requirements. But the surface of the moon’sglobe obviously affects her fitness, in one importantrespect, to be the abode of living creatures. Now theactual surface of the moon is rather more than twotwenty-sevenths of the earth’s, and the surface of theearth is about 196,870,000 square miles: hence themoon’s surface is about 14,600,000 square miles.This is about the same as the area of Europe andAfrica together (exclusive of the islands usually in-cluded with these continents). It is almost exactlyequal to the areas of North and South America ,exclusive of their islands. The portion of eitherhemisphere of the earth, lying on the polar side oflatitude 58° 23', is equal to the whole surface of themoon : that is, if E E', fig. 12, Plate I., represent theearth, P and P' being the poles, L Z and L' V latitudeparallels 58° 23' north and south of the equator E E',then either of the spaces of which L P Z, U P' Z' arethe visible halves, has an area equal to the moon’s.The arctic and antarctic regions together exceed themoon in area in about the proportion of 10 to 9.Lastly, it may be noticed that, reckoning the Russian