15 SEPTEMBER 1877, Page 8


AFL WENTWORTH ERCK, writing to Monday's Times 11'1 from the Observatory of Sherrington Bray, in the county of Wicklow, calculates the diameter of the outer satellite of Mars at about twenty miles. This is a good deal more than we ventured to suggest to our readers in writing on the satellites of Mars a fortnight ago, and we observe that Professor Newcomb, of the Washington Observatory, holds, with the accomplished writer of our own paper, that the diameter cannot be more than ten miles. But even granting Mr. Wentworth Erek's estimate, it appears to be quite legitimate to say of the satellite, as Mr. Wentworth Erek himself says, that it is—unless the inner satellite be a good deal smaller, which is not improbable- " by far the smallest celestial body known to us." Now, of course, we have no means of knowing whether there be or be not an atmosphere such as ours round this minute satellite, or whether it be, like our Moon, destitute of an atmo- sphere, and therefore, so far as analogy suggests to us, a mere 'plane-

tary cinder, without any room for the kind of organised life which depends on moisture, atmosphere, and oxidisation. But it is always instructive, as well as interesting, to notice how many conse- quences any single great change in one of the leading conditions of life brings with it, because it helps us to understand more distinctly the enormous wealth of resource in the universe, when we see how a variation in a single condition brings in its train changes so numerous and striking that the world in which they are realised mut present, even in its most superficial phenomena, the greatest contrasts to our own. We shall assume, then, that in the outer of the two newly-discovered satellites of Mara the diameter turns out to be (say) just twenty miles, that the density and surface of this satellite is, in other respects, not unlike that of Mara itself, that it is surrounded by an atmosphere, and that organised beings as rational as men live upon it, and then we shall just consider a few other of the vast differences which the great difference in magnitude between such a satellite and our own Earth, would bring with it.

In the first place, in a globe with only twenty miles from any place to its antipodes, the whole surface would not be greater than about 1,200 square miles,—or than the surface of such a county as Suffolk, for example,—and yet though so minute, it might perhaps contain all climates, climate depending chiefly not on the size of the planet, but on the angle at which the Sun's rays strike the surface. In such a petty world the whole circumnavigation of the globe would be only about as far as the voyage from Holy- head to Dublin, and hence the distance from the Equator to the Pole would not, if the little planet be nearly round, be above fifteen miles in all. Thus a walk of a single mile would take an inhabitant of this globule through six degrees of latitude, and in a three-mile walk it is therefore conceivable that he might change his latitude and his climate as vastly as an inhabitant of our earth who has sailed from London to Alexandria. In other words, the same change which can only be obtained in the same distance in our earth by climbing a high moun- tain, could be obtained there by an easy walk on the surface of the planet ; while a railway journey of the same distance which takes a man from 1tichmond or Twickenham to town, might on a little world of these dimensions take him from the temperate to the arctic or the torrid zone. Of course it is difficult to say how far mere minuteness of scale might not alter essentially the rules of temperature. It is difficult to suppose that mere contiguity would not itself prevent the great differences of temperature which are possible on a much larger globe. Granting even an exact paral- lelism in the causes at work, and no difference except the reduction of scale, you could not have as many zones of temperature in a pond four feet deep as you may have in the Atlantic or Pacific,— if only because heat is conducted much more rapidly, and is much sooner equalised, over a small surface than over a large. But making all proper allowance for this, any difference in temperature solely due to the angle at which the sun's rays strike down would be as great after a seven or eight-mile journey, north or south, in such a tiny world as this, as it would be on our own Earth after a journey of three thousand miles. Nor would this be the only extraordinary difference in the conditions of life due to this petti- ness of the world in which you lived. Supposing this little world to resemble our Moon in this, that it keeps always the same face turned towards Mars, just as our Moon always keeps the same face turned towards the Earth, then in a thirty-miles ride—or, if rail- ways existed there, and railways of our own average speed, in about an hour,—the inhabitant of this little world could exchange full sunlight for full or almost full Mars-light; and the surface of Mars, remember, being only at the distance of 12,000 miles, and his centre about three-and-a-half diameters of Mars, from this satellite, must exhibit an illuminated disc as large in appearance as fourteen hundred of our Moons. Or suppose the satellite to be in eclipse, enveloped in the mighty shadow of Mars itself, as it would be when it and the Sun were on opposite sides of Mars, then by a similar ride of thirty miles, the observer could plant himself on the clear side of the satellite, where the stars above his head would be those of the antipodes, and he would no longer have the sky above him half blotted out by the dark orb of the great planet round which

his own world circled. One hour's railway journey would take an inhabitant of this little world from the vision of the polar bear to that of the Southern Cross, or from that of Cepheus and Cygnus, his north polar constellations, to that of Indus et Pavo, in which lies his southern pole. Indeed, the rapid change of astronomical phenomena accessible to one who could travel as we travel, in such a dot of a world as this, would be something almost past our power of conceiving.

But this would be only a small part of the difference due to living in so minute a satellite. The weight of any given object on its surface (if we assume its consistency to be about the same as that of the Earth and Mars, which do not greatly differ in density) would be about four hundred times less than its weight on the surface of the Earth, so that the atmosphere which we assume it to have, would necessarily be a much rarer and also a much more widely extended atmosphere than any known to us. It is, of course, the attraction of the Earth which keeps our atmosphere so closely packed as it is. Diminish greatly that attrac- tion, and its particles would fly much wider apart, as indeed they do, as you approach the tops of high mountains. But if the atmosphere were far less dense, the clouds which it would have to carry, and the birds which used it for their flight, would also weigh so vastly less, that it would probably be as service- able for these purposes as before. Nevertheless, for the purpose of storing and retaining the warmth of the Sun, such an atmosphere. would not answer at all the same .purposes as ours, but would differ as much as a thin sheet differs from a warm blanket. Still more difficult is it to conceive how the architecture of swill a planet would be managed. The weight of materials has of course much to do with their solidity, but with weights four hun- dred times less, it is hard to conceive even a one-storeyed house holding together against any serious lateral blows. And yet, though in such a world the falls would be comparatively light, since the force of gravity would be itself so minute, there would. be no reason to suppose that the projectiles would be less deadly than in our own. Indeed, as the downward pull would be less, the range attained by any given projectile force, such as that due to kindled gunpowder, would be greater, and a Krupp cannon, for instance, would probably send its charge to a much greater distance, both because the resisting medium through which it passed would be less, and because the attraction of the little planet would not be sufficient to bring it so soon to the ground. Hence while the cohesion of the earthworks of such a world would be far smaller than here, the rending lateral pressures might be expected often to be greater, and to the engineer and the architect educated only in such a world as ours, this must suggest very difficult problems. On the other hand, the athletes of such a world, if endowed with anything like the same mechanical powers as we are, would surprise us by their high jumps. The Guy Livingstones of such a world, and the horses which they rode, would find it as easy perhaps to jump a mountain, as ours do to jump a five-barred gate. But it will be said,—What is the use of speculating on the con- ditions of a little world in which the population of Yorkshire would find themselves cramped and in need of all sorts of checks, —war, famine, or what you will,—to keep it down to the limits of the planet? Well, of course, the only use is to bring ourselves to see more clearly the endless variety of possible worlds, and to im- press upon ourselves that the least fundamental change in the con- ditions of life, involves thousands of others, the whole consequences of which it is hardly possible for us to reason out. But then, of course, it is easy to conceive that some one of these unforeseen differences might neutralise what seem to us theinconveniences of so confined a world. It is just conceivable, for instance, that the law of conflict for existence" on so small a theatre as that, would have weeded out all but the very finest organisations, and all organisations tending to multiply themselves at an inconvenient rate. In a population no bigger than that of Suffolk, or half or a quarter that of Suffolk (for some allowance must be made for the possible ocean of such a world), it is quite conceivable that you might have far more select minds and powers and higher mental resources, than we can muster amongst the whole population of our globe. It might well be that while we are painfully trying to permeate two or three great continents of petrified civilisations with the principle of progress, a few hundreds of families might there be all co-operating to carry thought, and knowledge, and worship into a region far higher than even the highest minds of our world can conceive. It is perfectly conceivable that, under different con- ditions, the highest concentration of mental resources into a small space would be far more favourable to further progress, than rela- tively large numbers with a relatively wide range, are to us. In a word, intensity of life in such a world might more than compen- sate for extension here ; and it is quite as conceivable that the highest point yet reached by organised beings might be reached in a globule such as this satellite of Mars, as it is that it might be reached in any of the Brogdingnagian worlds,—in Jupiter or Saturn, or the perhaps still mightier satellites of Aldebaran or Sirius.