Neptune are much larger; Mercury, Mars, the planetoids, and the satellites much smaller; Venus, our twin-sister world, almost the same. In form, the Earth is nearly a sphere, and so are all, or nearly all, its fellow-worlds; some are more flattened at the poles, and some less. The Earth is enveloped in an atmosphere,—so it seems are Venus, Mercury, Mars, and probably the giant planets Jupiter and Saturn. The earth has continents and oceans,—so have Mars and (probably) Venus. The Earth has snow in winter,—so it seems has Mars. The Earth possesses a satellite,—so do Mars, Jupiter, Saturn, Uranus, Neptune possess their satellites. In fact, the Earth is peculiar in nothing which we might expect to trace in other worlds. Why should we suppose it to be the sole abode of life? This subject has been much discussed. Not to speak of the older astronomers, in our own time Proctor, Flammarion, Brewster, and Powell have discussed it. I must own that the objections have ever seemed to me to be most frivolous. Can this grain on the sands of infinity—this little planet of an unimportant system—be the sole abode of vitality?
But, if there be life, what life? This is a question which has occupied many of the noblest of human minds. Man cannot know
