the most remarkable contrast to the planet Jupiter. For we have seen that Jupiter is very much larger than the earth, exceeding her more than twelve hundred times in volume, and more than three hundred times in mass or quantity of matter. Now Mars is very much smaller than the earth, being, indeed, much nearer to the moon both in point of size and in point of mass. In size he is about one-sixth part of the earth; in mass he is about one-ninth part. He is, in fact, the smallest of all the planets except Mercury (and of course the members of the ring of small bodies travelling between Jupiter and Mars). Moreover, he is contrasted to Jupiter in the fact that he has no moon, whereas Jupiter, as we have seen, is surrounded by a noble family of moons. What renders the contrast between these planets more remarkable is that they are next neighbours in the solar system, so far as the primary planets are concerned. According to the astronomy of Newton's day, and until the present century, there were in order the planets Mercury, Venus, the Earth, Mars, Jupiter, and Saturn; and thus, next to the two giants Jupiter and Saturn, but nearest of all to the greater giant Jupiter, there came the least of all the planets except Mercury.

But although Mars is a small and seemingly insignificant member of the solar family, he is in reality by no means the least interesting of the planets. He is, indeed, the one about which we know most. Venus comes nearer to us, but when she is nearest we cannot see her, since she

then lies directly towards the sun. Jupiter, again, looks larger than Mars, and we seem at first sight to perceive more in the belted globe of the giant planet than in the small red disc of Mars. But all the processes at work in Jupiter are seen under the diminishing effect of a distance. of some 360 millions of miles, whereas Mars, when favourably placed, is but some 50 millions of miles from us, on the average, and sometimes when he approaches at his very nearest, he is less than 40 millions of miles from us.

Under the telescope Mars presents appearances somewhat like those which we may imagine that our earth presents as seen from Venus or Mercury. There are reddish tracts which we may regard as the continents of the planet, and there are greenish regions which may very. well be oceans. Assuming this to be the case, we can note at once a marked difference between the arrangement of land and water in Mars and in our own earth. Our oceans exceed the continents nearly three times in extent. On Mars land and water are about equally divided. Again, the arrangement of land and water on our earth is such that in reality the continents may be looked upon as great islands. The two Americas form one great island. Europe, Asia, and Africa another; Australia a third; and then there are a multitude of smaller islands. In Mars a very different arrangement prevails. The relation is not absolutely reversed-that is to say, the oceans in Mars cannot be regarded as great lakes; but an intermediate

arrangement prevails, land and water being so intermixed that the great continents are connected with each other, as well as the great oceans. There are of course some islands and some lakes, but the chief divisions of land and water are connected as described.1

The next feature of Mars which has to be noticed is the presence of two white patches around the poles of the planet. These have long been regarded, and very reasonably, as the Arctic and Antarctic snows and ice fields of Mars. It occurred to Sir W. Herschel to study their appearance in order to see whether, as the Martial year progressed, they changed in size, waxing larger in winter and waning again in summer. For Mars has seasons as our earth has, his polar axis being sloped to the level of the path in which he travels, much as the earth's axis is sloped to the level of her path. The slope is rather greater, and therefore the seasonal changes must be somewhat more marked, but the difference is not very great. It follows that during the progress of the Martial year, which lasts 687 days, there must be spring and summer and autumn and winter in one hemisphere of Mars while in the other there are the seasons autumn, winter, spring, and summer. Now Herschel found, as he expected, that with the progress of these seasons the polar snows of Mars wax and

A coloured chart of Mars on the Stereographic projection is given in 'Other Worlds,' and a chart on Mercator's Projection in 'Orbs Around Us.' From these charts globes of the planet have been formed by Mr. Browning, the optician, and by Captain Busk (in the latter case Messrs. Malby have made the globes).

wane much as happens with the snow and ice in our own Arctic and Antarctic regions.

But even more like what takes place on our earth is the apparent formation of great masses of cloud, hiding from view the Martial lands and seas, sometimes for many successive hours. Indeed, it would seem that in the winter season of Mars the sky is commonly overcast, for the features of the winter half of the planet are not nearly so well seen as those of the half where summer is in progress. And then again it would seem as though at early morning and again in the evening fogs and mist prevail in Mars, for the parts of the planet which have lately come into sunlight, as well as those which are about to pass away to the night half of the globe, always show a whitish light which altogether conceals the features of land and water.

Perhaps, however, the most remarkable circumstance. of all in connection with the ruddy planet is the fact that astronomers have been able to prove that there is water on Mars. The mere appearance of greenish tracts on the planet may suggest the idea that water exists there; but yet we could not be at all sure that this is the case. Again, the white polar caps of Mars are very well explained by the supposition that they are snow-covered regions; yet this supposition might be altogether erroneous. And it might seem as though nothing short of a visit to Mars could place the existence of water on the planet's surface altogether beyond dispute. But by means of the wonder

ful powers of the new instrument of research called the spectroscope, it has been proved beyond all possibility of question that there is water on Mars. The way in which this has been done is in reality sufficiently simple, though it would not be easy to explain it fully in these columns. This much, however, may be said in the way of explanation. When the sun's light is examined with a spectroscope, the white sunlight is changed into a rainbow-tinted streak crossed by a multitude of dark lines. When the sun is low down, so that his light traverses the lower parts of the air, certain new dark lines and bands are seen in the rainbow-tinted streak called the solar spectrum; and it has been proved that some of these new lines are solely due to the vapour of water in our atmosphere. Now, the light of Mars is reflected sunlight; and therefore when examined with the spectroscope, it gives the rainbowtinted streak and the dark lines which form the solar spectrum. But also it gives the dark bands known to belong to the vapour of water; and these bands are seen when Mars is high above our horizon, so that the bands cannot be due to the vapour of water in our atmosphere. Hence it follows that there is the vapour of water in the atmosphere of Mars. This vapour can only be raised (in sufficient quantities) from the surface of seas and oceans; hence we can infer safely that the greenish tracts are oceanic. And it is clear that, having moisture in the Martial air, we should expect cloud, rain, and snow