atmosphere above it 200 thousand feet high at least, and it may be, much more. And this being so, if we increase the depth of the centre 20 thousand times; if we carry the extreme verge of air and vapor to thirty times the radius of the earth's orbit from us, how does the construction of the machine become more improbable, or the disproportion of its size to its purpose more incongruous? Is mere size,--extent of brute matter or blank space,--so majestic a thing? Is not infinite space large enough to admit of machines of any size without grudging? But if we thus move the centre of the Earth's peopled surface 20 thousand times further off, we reach the Sun. If we carry the limit of air and vapor to the distance of 30 times the radius of the Earth's orbit we arrive at Neptune. Are these new numbers monstrous, while the old ones were accepted without scruple? Is number such an alarming feature in the description of the Universe? Does not the description of every part and every aspect of it, present us with numbers so large, that wonder and repugnance, on that ground are long ago exhausted? Surely this is so: and if the evidence really tend to prove to us that all the solar system ministers to the earth's population; the mere size of the system, compared with the space occupied by the population, will not long stand in the way of the reception of such a doctrine. 8. But the objection will perhaps be urged in another form. It will be said that the other Planets have so many points of resemblance with the Earth, that we must suppose their nature and purpose the same. They, like the Earth, revolve in circles round the sun, rotate on their own axes, have, several of them, satellites, are opaque bodies, deriving light and probably heat from the sun. To an external spectator of the Solar System, they would not be distinguishable from the Earth. Such a spectator would never be tempted to guess that the Earth alone, of all these, neither the greatest nor the least, neither the one with the most satellites, nor the fewest, neither the innermost nor the outermost of the planets, is the only one inhabited; or at any rate the only one inhabited by an intelligent population. And to this we reply; that the largest of the other planets, if we judge rightly, are _not_ like the Earth in one most essential respect, their density; and none of them, in having a surface consisting of land and water; except perhaps Mars: that if the supposed external spectator could see that this was so, he might see that the earth was different from the rest; and he might be able to see the vaporous nature of the outer planets, so that he would no more think of peopling them, than we do, of peopling the grand Alpine ridges and vallies which we see in the clouds of a summer-sky.