when he has travelled round to the opposite side of the Sun, turning towards him the south pole, summer reigns over the southern half and winter grips the northern half.

And the two poles of Mars are clothed, each one, with a white cap. Snow and ice, of course! Well, not quite "of course." Through many years doubts were freely expressed, and other possible substances, in place of water, such as carbonic acid, were discussed.

Now, however, it seems pretty generally accepted as fairly certain that those white caps really and truly are ice and snow, like our own northern and southern ice-caps !

During the summer of each pole in turn, when that pole is turned towards the Sun, its ice-cap grows visibly smaller; and during the winter of each pole, when that pole is turned away from the Sun, its ice-cap grows visibly larger. These changes have been again and again noted, and the varying sizes of the ice-caps have been measured.

Thawing is sometimes seen to take place very quickly. In only six days the boundary-line of one cap shrank to an extent of six hundred miles. So great a mass of snow would result in a huge volume of water.

Clouds seem to be fairly common; not vast masses like those which clothe Venus, but extensive enough to be seen from Earth. They change and grow and melt away, much as our clouds do.

And if there is an atmosphere, and if there are clouds and snow, we may be sure that there is also rain, perhaps in parts very heavy rain. Which makes it probable that floods take place at times. And this, again,

would mean the movement of big supplies of water from one place to another.

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Among the varied tints and dim outlines seen on Mars, parts were long looked upon as "land" and "water." This in time was given up, and the notion of any kind of oceans was scouted. But another modification has crept in; and while it is still held that no large permanent oceans are found, yet bodies of water do exist. The melting of hundreds of square miles of snow, even though the snow may not be very deep, would ensure such a result.

Such "seas," as they are often called, are sometimes seen to grow at a startling rate. In one place, on a certain day, no signs of water were visible. But within three days a considerable lake had made its appearance there, hundreds of miles long and broad. Judging from its bright surface and its blue colour, little doubt could be felt that it really was water.

"Within my breast there is no light,
But the cold light of stars;

I give the first watch of the night
To the red planet, Mars." 1

LONGFELLOW.

III. CANALS AND MARSHES

Some curious straight lines have been seen from time to time on Mars, claiming attention. It was long questioned whether they meant anything real—whether they might not be due to imagination. But there the lines are, unmistakably; and they certainly mean something.

A rather unfortunate name was given to them at the first, and it has clung ever since, as the most meaningless names have a trick of doing. They were called CANALS.

Our earthly conception of a canal is an artificial watercourse made by man. Naturally, people in general at once supposed that canals on Mars must be the same in kind, made by beings such as ourselves. Certain astronomers have warmly upheld the idea, while others have refused to accept it as even probable.

We sometimes speak of "Martians," as if we knew that they really existed. Of course we do not know. They may be there. No human being can declare that it is impossible. Eut we have no reliable proofs whatever that it is so, though certain indications may seem to point to the possibility. At the best, we can only suppose, and imagine, and conjecture.

1 This ruddy world-which, despite all poetic assertions, is no star-was named after "the god of war," the Mars of ancient mythology.

At first only two or three lines were seen; but as time went on, and observations also went on, many more were detected, till at length a real network of them could be drawn over the face of the planet, looking not unlike a spider's web. Some astronomers see them very clearly. Others have frankly confessed their inability to make them out at all.

The first point which struck everybody was their extraordinary straightness; and this it was, no doubt, which first suggested the notion of "canals.” Still, it must be remembered that "straightness" in objects tens of millions of miles distant does not, or need not, mean the same as straightness in an object near at hand. A river, seen on Earth from a distance of one or two hundred miles, would probably look straight; yet, when viewed from near at hand, it would have any number of bends and curves.

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These "canals" were at first regarded as almost certainly whether natural or artificial-intended for the carrying away of melted snows from the north pole, southward; and perhaps also for the support of vegetation.

Then doubts arose. It was found that a canal would sometimes run right through a part which had been looked upon as a probable sea. This, if the sea were really a sea, would pretty well prove that the canal was not a canal. Or, if the canal were really a canal, it would prove that the sea was not a sea. Again, it appeared that the so-called "canals " were not always fixed in certain places, but that some of them seemed to change their positions, to shift about, to disappear and re-appear, perhaps following fresh courses.

All these things were puzzling. Moreover, the canals were found to be much bigger than was first imagined; much longer, much broader. It became difficult to think that any beings like ourselves could have constructed them.

It is still held that they may be channels, which serve to carry off masses of water from the polar regions, perhaps depositing that water in large lakes or sea-beds. But another difficulty comes in here. If Mars is so very flat a world as it seems to be, there can be little of uphill and downhill; and how, then, could water in large quantities flow constantly from one part to another? The idea reminds one of a phrase used by Robert Montgomery in one of his poems, and mercilessly criticised by Macaulay—

“The soul aspiring, pants its source to mount,
As streams meander level with their fount."

"No stream meanders, or can possibly meander, level with its fount," declared the indignant Essayist. If so, how do the streams find their way in Mars?

A new suggestion has been more lately made. What if, in place of being something in the nature of canals or rivers, these long lines are really somewhat extensive marshes; not so much carrying onward but rather holding back the supplies of water from snows and rains? Perhaps the real danger is of such water disappearing too quickly into the atmosphere, or spreading about too quickly in thin layers, easily dissipated. Without some sort of natural—or, if you like, artificial"reservoirs," this might take place. If such be the