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11, 1863.] revived in France, and spoken of as something quite novel.

Assuming the above theory to be true, the same process would be repeated as the sun continued to revolve and scatter its heat through space, and the planet Uranus would be formed. A repetition of it would produce Saturn, next Jupiter, then the huge planet, or the bodies that may once have been one, the Asteroids; then Mars, the Earth, Venus, and Mercury in succession, and, possibly, another planet within the orbit of Mercury, which from its proximity to that luminary is invisible to us. Assuming that we have now positive evidence that all the metals with which we are acquainted exist in a state of combustion in the sun’s atmosphere, and having regard to the physical appearances discernible on the planets belonging to our system, it may fairly be inferred upon this principle that they are all composed of similar substances. The question of their adaptability to the residence of organised beings, not differing essentially from ourselves, therefore would rest on their bulk, on the amount of light and heat they receive from the central orb, and on the presence of an atmosphere.

First, as regards their bulk. The weight of an object on the Earth is in proportion to the density of the globe and the distance of the object from its centre. The same holds good with respect to Jupiter, which is thirteen hundred and thirty times larger; and supposing the densities of both to be alike, the consequence would be that any object whatever, whether a man, a tree, or one of the pyramids, transported hence to that planet would crumble to pieces under the force of the attraction. But the densities of the planets are not equal. Taking first the exterior planet, Neptune, it is found that, bulk for bulk, its weight as compared with the Earth is as one to six, or nearly that of water, which is five and a half times lighter than the solid matter contained in our globe. Thus, though the bulk of Neptune is 107 times that of the Earth, its relative lightness, combined with the fact that an object on its surface is nearly five times more distant from its centre, would cause bodies to weigh nearly the same there as here. We will make this matter a little clearer to those who have not considered the subject.

If the density of Neptune were the same as the earth, bodies placed at the same distance from its centre would weigh 107 times heavier than here. But as the weight of a body, or the force with which it is drawn towards the centre of the globe on which it rests, is diminished in proportion as it is more distant from the centre of attraction, a deduction would have to be made on this account, so that a man who weighed 150 lbs. on the Earth would actually weigh only 700 lbs. on the surface of Neptune. This is calculated on the supposition that the density of Neptune is the same as that of the planet we inhabit. The fact, however, is, as we have already said, that in consequence of the lightness of Neptune as compared with the Earth, a man going hence to that globe would be able to move with the same facility. As regards Uranus, though its dimensions are eighty-two times that of the earth, its weight, as compared with it, bulk for bulk, is not greater than that of Neptune, that is to say, as one to six, or a little less than water. The same powers of locomotion would therefore suffice if a man were transported to Uranus. Saturn is comparatively much lighter than either of the planets previously mentioned; they are of nearly the same weight as a globe of water would be, whereas Saturn is lighter in the proportion of one to one-and-a-half. But as its volume is 857 times that of the Earth, the actual weight of a man on its surface would be somewhat greater than on this globe, but not in a degree capable of impeding his movements to any serious extent.

The enormous dimensions of Jupiter, notwithstanding its lightness as compared bulk for bulk with the Earth, would render a residence on it irksome, though not impossible, without an increase of muscular power. On Mars half the strength we possess would be sufficient to enable us to move about and supply our wants with facility. The same may be said of Mercury: and as regards the only other planet of our system not yet mentioned, Venus, we should there be unconscious of having changed our habitation, as far as bodily strength is concerned.

We do not see, in the lightness of the majority of the planets as compared with our own globe, any ground for the inference that they are thereby unfit for human habitation, since lightness is quite compatible with solidity. The other objections that might be urged are, that there would be an insufficient supply of light and heat to support life on planets revolving at such an enormous distance from the central orb whence that light and heat emanates. At the first glance it would seem that if we have not a superabundance of either it must follow that Jupiter, which is five times more distant, must be deficient in both; and that this deficiency must go on increasing in an eminent degree as we recede to Saturn, which is nine times, to Uranus, which is eighteen times, and to Neptune, which is twenty-eight times more distant than the Earth. But a little consideration will show that, though regarded with our organs of vision, the sun, seen from Neptune, would appear of about the same diameter as a bright star, an enlargement of the pupils would cause objects on its surface to appear as brilliantly illuminated as on the Earth; the same result would be produced if the retina were rendered more sensible, either of which modifications might be produced without any alteration in the structural organisation of the eye.

But the most important question of all is: Have the other planets an atmosphere resembling ours? If they have not, it is clear that, however closely they may resemble the Earth in other respects, they cannot be inhabited by beings like us. If we were deprived of our atmosphere we know that there could be no clouds, no gradual passage from light to darkness; objects would be strongly lighted or in deep shadow, the sun would