non to be this, that the morning and evening skies of the Martialists are more clouded than the midday sky: a condition which is known to prevail in certain seasons and latitudes on our own earth also. The indistinctness of the wintry hemisphere points to the prevalence of cloudy skies during the Martial winter; and this peculiarity is not only conformable with recognised habitudes on our own earth, but corresponds with the variations of the Polar snow-caps. 'The enormous transfer of moisture from one hemisphere to the other,' writes Professor Phillips, while the snows are melting round one pole and forming round the other, must generate over a great part of the planet heavy storms and great breadths of fluctuating clouds, which would not, as on the quickly rotating mass of Jupiter, gather into equatorial bands, but be more under the influence of prominent land and irregular tracts of ocean.'

But the strongest argument in favour of a similarity in general physical relations between Mars and our own earth, is drawn from the revelations which have been afforded by the spectroscope. This evidence has been discussed with considerable fulness in my work entitled Other Worlds than Ours.' Those readers who are anxious to examine the subject more at length, should read Dr. Huggins' paper on the spectrum of Mars, in the Monthly Notices of the Royal Astronomical Society' for 1867. The main facts pointed to by his researches are the following:-First, the red colour of Mars is not due to an absorptive power in his atmosphere, resembling that in our own

air which causes the ruddy skies of twilight. If this were so, the snowy poles would lose their white colour, since we see them through the densest strata of the Martial atmosphere. But secondly, although the atmosphere around Mars is not so abnormally dense as to produce the ruddy tint of the planet, yet that atmosphere does contain gases and vapours corresponding to those which are present in our own air; for lines appear in the spectrum which correspond with those which appear in the solar spectrum when the sun's light traverses the lower strata of the earth's atmosphere. That these lines,' says Dr. Huggins, were not produced by the portion of the earth's atmosphere through which the light of Mars had passed, was shown by the absence of similar lines in the spectrum of the moon, which at the time of observation had a smaller altitude than Mars;' so that, if the lines had been due to the earth's atmosphere, they should have been stronger in the moon's spectrum than in that of the planet.

6

It appears, then, from the searching scrutiny of the spectroscope, that Mars has an atmosphere, and that that atmosphere most probably resembles our own in general constitution. Combining this evidence with that which we already possess of the presence of water in its liquid, vaporous, and solid states, upon the surface of Mars, and with the certainty that the red tint of parts of the planet is due to a real ruddiness of substance (corresponding to the tint of certain soils upon our own earth), we cannot but recognise the

extreme probability that in all essential habitudes the planet Mars resembles our own earth. One circumstance may at first excite surprise: the fact, namely, that in a planet so much farther from the sun there should exist so close a resemblance to the earth, as respects climatic relations. But if we consider the results of Tyndall's researches on the Radiation of Heat, and remember that a very moderate increase in the quantity of certain vapours present in our atmosphere would suffice to render the climate of the earth intolerable through excess of heat (just as glass walls cause a hot-house to be warm long after the sun has set), we shall not fail to see that Mars may readily be compensated by a corresponding arrangement for his increased distance from the vivifying centre of the solar system.

123

A MINIATURE SUN.

VENUS herself, when seen under most favourable conditions, scarcely exceeds in brilliancy the giant planet Jupiter; and there are times when, setting aside telescopic aid, even the practised astronomer can only distinguish her from his beautiful orb by a certain faint tinge of yellow which characterises her lustre. Far more distant than she is, both from us and from the sun, and far less brilliantly illuminated, Jupiter makes up, or nearly so, for both these circumstances by his mighty bulk, and also, as will presently appear, by a peculiar light-giving power, which distinguishes him from the Planet of Love.

I purpose to give a brief account of some of the characteristics of the noblest planet of the solar system, and then to consider certain circumstances which have received far less attention than they deserve. And although in the course of this paper I shall have to refer to several details which I have already dealt with at length in Other Worlds than Ours,' yet I shall, for the most part, direct the reader's attention

When this paper appeared there were two Evening StarsVenus and Jupiter shining with rival lustre in the western sky. The two planets were quite close to each other on May 12, 1871, Jupiter afterwards passing away from Venus westwards.

to new evidence-in fact, to considerations which have occurred to me, or have been discussed by others, since the second edition of that work was published.

Jupiter is a globe exceeding our earth some twelve hundred times in volume, but made of matter whose average density is so much lighter than the earth's that his weight exceeds hers but about three hundred times. Let this last point not be misunderstood, however. It can by no means be asserted that the matter composing Jupiter's globe is lighter-bulk for bulk— than our rocks, or even than our metals. It is only on the average that he is of small density. We may put the matter thus. A globe as large as Jupiter seems to be, if made of some substance about one-fourth heavier than water-bulk for bulk-would be equal to Jupiter in mass or weight; whereas a globe as large as our earth is known to be, would have to be made of a substance more than five times as heavy as water to equal her in mass.

Jupiter is more than five times as far from the sun as our earth is; and, instead of one year, he occupies nearly twelve years in travelling once on his path around the ruling centre of the planetary scheme. As he speeds along his noble orbit he rotates very swiftly; so that, notwithstanding his giant bulk, he turns completely round upon his axis about five times during the interval which this little earth occupies in making two rotations-that is, during two days.

Jupiter is attended by no less than four moons. It has been said that these moons are made of even