who weighs 150 pounds on the Earth, if transported to Jupiter, would shake the ground with a ponderous tread of 45,000 pounds, or 222 tons! His own weight would at once crush him into a mere pulp. A hickory-nut, falling from a bough, would crash through him like a Minié-ball. Again, water would weigh fifteen times as much as quicksilver. A moderate wave would shiver to atoms the strongest ironclad, a rivulet would quickly form canons miles deep, and ordinary hailstones would destroy every living thing. If we suppose the existence of an atmosphere, even no more profound than our own, its weight would be a third that of water, and its pressure 4,500 pounds to the square inch—sufficient to crush a rhinoceros or the boiler of a steam engine. In motion, as a moderate breeze, it would sweep away not only every work of man, but the very hills and mountains. The same condition, in less degree, may be predicated of the lesser of the giant planets, and Jupiter is only selected as the most striking example.
Putting aside the hundreds of known, and the thousands and millions of unknown asteroids, as obviously unfit for life, let us next consider the case of Mars. The relative mass of Mars being only about 60 that of the Earth, it follows, as a necessary consequence of the laws of gravitation, that our typical man would only weigh about 22 pounds on the surface of that planet. Individual locomotion would be wonderfully facilitated, but its conditions would be reversed. The familiar dream of flying by a mere upward movement of the limbs might easily be realized in Mars, but an 80-ton locomotive would not propel a train of empty cars, and mechanical work of all kinds would be practically impossible. Niagara Falls, in such a planet, with water approximating the weight of air, would scarcely furnish power for a mill. A rifle ball might be caught in the hand without harm. It is obvious that, with an atmosphere of the density of our own, animal and vegetable life, and every artificial work, representing so many structures of gossamer, would disappear like magic at the first breeze. But no such atmosphere as ours is possible with Mars. Even supposing it to equal our own in altitude, its pressure would be only about one fourth of a pound to the inch. Life is impossible in such an atmosphere, as is shown by a far less tenuity at the summits of lofty mountains. But, even if gravitation were not deficient, the distance of Mars from the sun entitles him to considerably less than half our supply of light and heat; a disadvantage immensely aggravated by his very eccentric orbit. Croll has shown how the shifting eccentricity of the earth's orbit, by adding three weeks to the duration of winter, brought about the glacial epochs, and covered nearly the whole earth with ice at various eras. Conceive, then, the thermometer in the Martial torrid regions touching 50°, and that even under the hypothesis, rendered impossible by the very laws of gravitation, of an atmosphere as dense as our own! Nothing can be more certain than that there is no liquid in Mars, and no life.