were

in addition, show the seas and continents of the planet to great advantage. In those three instances the snow-zones touching the margins of the planets, but in the second figure (taken by the writer on April 23, 1856, with the great Cambridge Equatorial) the south, or uppermost pole, was quite isolated. As a proof of the brightness of the snow-spots, it may be mentioned, that on this occasion, when a cloud passed over and completely obliterated the planet, the snow-zones were quite large and bright, and appeared like faint stars struggling through the mist.

Let us follow those spots through their regular changes. The planet comes into view on the Earth; the northern part, after a winter season about as long as one of our years, again receives the beams of the Sun. The patch of snow, as it appears to us, at first large, diminishes gradually, and finally vanishes. After having had the companionship of the stars and of the night for a great interval, and passed a long period under the dominion of darkness, the Sun appears, and to the protracted night succeeds the equally long day, with its fierce heat and light. Nothing occurs between the fiery summer and the bleak and dark winter; the other two seasons are wanting, but the one which is present amply makes amends for those which are absent, by the intense changes which take place in a comparatively short time. The Arctic seas, which were previously blocked up with solid ice or frozen snow, and have stopped the passage by sea and land, are gradually thawing; the Northern again becomes liquid, the snows melt, the ice passes into its primeval condition, the land becomes passable, and the Sun-the cause of all this commotion-keeps in sight all day long, as if to tyrannize over those whom it has previously, by its absence, subjugated. The air becomes clearer, fogs have disappeared, the seas and continents have apparently a clear atmosphere overhead,-if we are to judge by the facility with which we view them, the November mists and murky atmospheres have been succeeded by a dry air and sunny skies. The opposite changes take place in the southern hemisphere, whilst these variations are progressing in the northern. In the former, however, the extremes of heat and cold will be more severely felt. From the great eccentricity of Mars, the distance of the planet may vary between 131 and 158 millions of miles from the Sun; but when it is summer in the southern hemisphere, the Sun is nearest the planet; when winter, it is farthest from it. The quantity of heat and light received at those times by the southern portion of the planet are respectively 0.52 and 0.36; that of the Earth being 100. The consequence is, that the summers are hotter and the winters colder on the southern than on the northern hemisphere. This is confirmed by observation; for whilst the

VOL. II.-NO. VI.

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northern patch of snow varies but slightly in dimensions, the southern is of great size in the winter, and almost vanishes in

summer.

From the foregoing facts, and the deductions which may naturally be drawn from them, the reader has ample means for judging, in this individual instance at least, as to the probability of the planets being the abode of animal and vegetable life. It would be impossible, of course, to give any minute details on this point, to say that such a place is forest land, or cultivated ground, or artificial formations; for when Mars is nearest the Earth-making use of the most powerful telescope yet constructed, the observer is merely able to tell whether a space of ground which is two hundred miles long by two hundred broad, or an area of 40,000 miles, is round or square. From this circumstance, the observations of Schroeter, who saw clouds passing over the planet with a velocity from forty to sixty times that of the most violent hurricanes on the Earth, have been much doubted. But otherwise we have every evidence of an atmosphere, of snow, of changeable weather, of bright and sunny skies, of the existence of water. The seasons, though not so equable in duration as those on the Earth, are still present, with all their agreeable changes; we see the seed-time and harvest, the ripening summer and the dark winter. The isothermal lines on the Earth are reproduced on Mars, if we are to judge by the position of the snow-zones, which are not placed exactly at the poles. Nor does the excessive cold which might be surmised to take place from the planet's distance from the solar heat really appear to be so severe. Whether, from some peculiarity in the atmosphere, the latent heat of the body itself, or other causes unknown to us, the polar snows do not appear of the vast extent which might be imagined. Even those thaw away with a rapidity which seems marvellous, whilst the equatorial regions are altogether free from such visitations. Venus receives four times the heat of Mars, and twice that of the Earth; yet at the North Pole of Venus, a bright white and large spot has been perceived, which may naturally be surinised to be of the same nature as the snow-capped poles of the Earth and Mars; and we might from this conclude that no great difference exists in those three planets at least, whatever may be the case in the other two groups of planets,-i.e., the seventysix asteroids, or the huge exterior planets of small density, quick rotation, and accompanied by numerous moons and a ring.

The diameter of Mars is about twice that of the Moon, and more than one-half of that of the Earth. Its surface is about four times greater than that of the former, and is one quarter that of the latter. Bulk for bulk, Mars is seven times larger than the Moon, and the Earth is seven times larger than Mars.

Weight for weight, the Earth is more than seven times heavier than Mars. It would take upwards of two and a half millions of bodies like Mars to counterpoise the weight of the Sun. We thus see that Mars, with its diameter of 4,100 miles, holds a geometrical mean between the Moon and the Earth. The attraction, fall of bodies, and length of pendulum, are about onehalf of what those are on the Earth. Unlike the latter body, it has no satellite, although, if this latter were thirty miles in diameter, it could not pass unnoticed.

Maedler has calculated the duration of the seasons in Mars, which are as follows:

دو

From Spring to Summer (Spring in North, Summer in South), 191 days. Summer to Autumn (Summer in North, Winter in South), 181 Autumn to Winter (Harvest in North, Spring in South), 149 Winter to Spring (Winter in North, Summer in South),

147

It will thus be seen that there are 372 days of spring and summer in the northern, and only 296 days in the southern hemisphere. The winter in the north only lasts 147 days; in the south 181 days. The heat and light in the northern summer is as 20 to 29 to the south. The consequence of this will be, that there is a long temperate summer, and a short mild winter; whilst in the southern, there will be a short hot summer, and long and severe winter.

The sixth figure gives a map of one of the hemispheres of Mars, as drawn by Maedler, and shows what may be done by means of a small telescope. The seventh and eighth figures represent the opposite hemispheres of the planet as drawn by the writer on December 10, 9h. 20m., and November 22, 10h. P.M., 1862. The spots in the seventh figure would appear to be the best defined of the planet, and bear a striking resemblance to those seen in 1719 by Maraldi, on August 19 and 20, and September 25 and 26, as also to that seen by Sir W. Herschel on October 10, 1783, at 6h. 55m. P.M.