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IV.

How hot it was ! Across the white-hot wall

Pale olives stretch towards the blazing street;
You broke a branch, you never spoke at all,

· But gave it me to fan with in the heat ;
You gave it me without a sign or word,
And yet, my love, I think you knew I heard.
You gave it me without a word or sign :
Under the olives first I called you mine.

V.

At Lucca, for the autumn festival,

The streets are tulip-gay; but you and I Forgot them, seeing over church and wall

Guinigi's tower soar i' the black-blue sky, A stem of delicate rose against the blue, And on the top two lonely olives grew, Crowning the tower, far from the hills, alone, As on our risen love our lives are grown.

VI.

Who would have thought we should stand again together,

Here, with the convent a frown of towers above us ; Here, mid the sere-wooded hills and wintry weather ;

Here, where the olives bend down and seem to love us ; Here, where the fruit-laden olives half remember All that began in their shadow last November ; Here, where we knew we must part, must part and sever ; Here where we know we shall love for aye and ever.

VII.

Reach up and pluck a branch, and give it me,

That I may hang it in my Northern room,
That I may find it there, and wake and see

-Not you ! not you !-dead leaves and wintry gloom.
O senseless olives, wherefore should I take
Your leaves to balm a heart that can but ache?
Why should I take you hence, that can but show
How much is left behind? I do not know.

A. MARY F. ROBINSON,

SCIENCE NOTES.

THE THREATENING COMET.

AT

T the termination of the Roman Carnival of 1843 I started on

foot to Naples, my companions being C. M. Clayton, of Delaware, a son of the statesman who negotiated the Clayton-Bulwer Treaty, and another American from the South. We arrived at Naples on March 10th. The sky was clouded then, but a night or two afterwards we were startled by a strange apparition in the sky. Stretching along the heavens in the line of the Strada Toledo, directly between the house-tops, and extending the whole apparent length of that main highway, was a phosphorescent cloud, which neither of us could understand.

It stretched over fully two-thirds of the whole sky-arch. We had heard and read of comets, but this was quite a different thing from our ideas of a comet. It had no visible structure, and no decided head; it was merely a luminous mist, two or three degrees (about five moons' diameters) wide, and sixty-five degrees long. We had walked through a region where newspapers were unknown, and had heard of no comet. On consulting Galignani, we found that it really was a comet; but the sight of such a comet greatly expanded our notions of these bodies.

This comet has just made another appearance among us, not in the heavens this time, but lower down, in the newspapers. Mr. Proctor has republished in his last book, “ Familiar Science Studies,” an essay on "A Menacing Comet," and several papers have discussed Mr. Proctor's view, some thoughtfully, others with that professional flippancy and cool assumption of superiority which a well-trained journalist so skilfully adopts when commissioned to write upon a subject of which he is utterly ignorant, or to review a book which he cannot understand.

Mr. Proctor states good astronomical reasons for supposing that the comet of 1843 was the same that appeared in 1688, and that the comet of 1880 was another revisit of the same. Those who desire to follow up the reasoning upon which these conclusions are based

should read the essay. I may merely add that Mr. Proctor explains the great discrepancy of the intervals between 1688 and 1843, or 175 years against 37, by the fact that in 1843 the head of the comet came so near to the sun that it must have swept through that outspread of solar matter, the corona; in doing which, it encountered a resistance that must have checked its velocity, and therefore have shortened its orbital journey.

But in 1880 it rushed through the corona again, hereby receiving another check that must still further contract its path. Thus, according to Mr. Proctor, we may expect it again in 1897, or thereabouts ; but then it will have lost so much of that tangental momentum which has hitherto carried it past the sun, that it may possibly succumb to solar gravitation, and fall into that luminary instead of brushing through its atmospheric fringe.

So far I follow and understand Mr. Proctor's reasoning, but when he describes its probable results I find that my conceptions of what may occur are widely at variance with his.

He calculates the velocity of a comet's motion, and the calorific effect of arresting this motion by its fall into the sun, and maintains that "if at any time a great comet falling directly upon the sun should, by the swift rush of its meteoric components, excite the frame of the sun to a lustre far exceeding that with which he at present shines, the sudden access of lustre and heat would prove destructive to every living creature, or at any rate to all the higher forms of life upon this earth.”

Mr. Proctor does not absolutely predict this effect from the particular comet in question, as the newspapers assert, but speaks generally, and I disagree even with his general view of the subject, as the following Note will show.

MY VIEW OF COMETARY COLLISION WITH THE SUN.

A

COMET is a collection of discrete cosmic fragments of some

kind, a cloud of meteoric dust, the particles of which probably emulate the doings of solar systems, of primaries and satellites, by having little orbits of their own around the common centre of gravity of their special little system. Thus moving among themselves they travel round our sun, or some other sun, as our sun travels with all his dependent worlds, &c., around some mightier undetermined centre. When these miniature systems come so near to the sun as the visible comets usually do, they are seriously disturbed by volatilisation, coronal friction or otherwise, as indicated by the

observed distortions and outstreamings of cometary heads or nuclei, when approaching perihelion. I have used a little imagination to fill up this sketch, but I think not illegitimately. Let us now apply it to the case of the comet of 1843, to that of 1880, and its threatened return in 1897 or sooner.

The tail of the comet of 1843 was about 150 millions of miles in length, and two to three millions of miles wide. The breadth at the head was about the same, but the breadth of the head is not so easily determined, seeing that its boundaries are not definable. Let us suppose that some of the actual material extended to a distance of a quarter of a million of miles from the centre of the nucleus, that some outer particles travelled in an orbit of 500,000 miles in diameter, one-fourth of the apparent diameter of the head. I make this moderate supposition because the tail of a comet cannot be made up of what we understand by "matter," and such is probably the case with much of the coma or luminosity around the nucleus.

The orbit of the comet, i.e. the centre of gravity of the whole assemblage of particles, came within 190,000 miles of the sun's surface, and thus, if it had the diameter above-named, a considerable portion must have been left behind, actually swept into the sun.

This may account for the diminished magnitude of the comet's reappearance in 1880, assuming it to be the same, and for the strangely shorn dimensions of many other great comets when they have revisited the fringes of the sun. In 1880 it again grazed the sun in like manner, and probably with a similar result. Therefore when it comes again we may expect that it will be smaller still, and then leave some more fragments behind, and then come back again a mere pigmy, and perhaps again and again, before being all absorbed.

If I am right, we are threatened, not with one great cometary crash, but merely with a series of cometary dribbles, producing in the sun meteoric showers similar in kind to those which visit our atmosphere, but of vastly greater magnitude ; and this, I think, must be the usual course and manner of cometary collision with the sun.

Astronomers are now generally agreed in regarding the meteors which we encounter in certain tracts of space as the trails (not the tails) of comets, i.e. portions of the actual body of the comet itself, and therefore fair samples of the bulk.

In spite of the display made by these meteors on certain memorable occasions, we have never been able to trace any appreciable thermal effect produced by them on our climate, even when thus actually in our atmosphere. This probably arises from their miere dust like magnitude. The explosion of the head of a lucifer match makes a great display in a dark room, without sensibly raising its temperature, and the brilliant celestial fire-works due to cometary fragments are similarly ineffective.

Comets are really impostors, making a big blaze with very little substance. Stars that are hidden by the thinnest haze of cirrous cloud have been distinctly seen right through the centre of a comet's head, and when comets do afford us an opportunity of weighing them by observing their gravitating disturbance on other celestial bodies, the sum total of their weight is too small to turn the scale of the most delicate astronomical balance. All that we know of comets and of their meteoric tails that visit our earth indicates such a merely cloudlike structure, that even the direct plunge of a whole comet point-blank at the sun (and this is what Mr. Proctor described as dangerous) would merely produce a brilliant luminous display due to intensity of ignition rather than to quantity of thermal energy.

From all these considerations we are, I think, justified in expecting, on the return of the flimsy phantom of 1880, nothing more than a solar meteoric shower about sufficient to cancel the sun-spots otherwise due. Such a cancelling did actually occur in 1880, when the usual sun-spot cycle should have commenced, but for some reason, hitherto unknown, it was postponed. The dark cavities may have been filled up or bridged over by the blaze of the colliding cometary particles.

As regards the probable effect of such an increase of solar heat upon the earth, I must refer the reader to my Science Notes in the Gentleman's Magazine for August 1881, where I have endeavoured to show that our strange weather of 1880-1 was due to increased solar activity during our winter time when the sun was at work over the southern hemisphere. In another Note on “The Coming Winter" in last November's number, I proceeded further with the same argument, and ventured upon it to base some predictions that have been since verified with curious exactness.

In considering possible variations of solar activity and their effects on the earth, we must never lose sight of the fact that our world as presented to the solar rays is mainly a world of water ; threefourths is actually covered by ocean and lakes, and the other quarter, which we call dry land, is decidedly moist, exhaling watery vapour from its own surface and from that of the vegetation which covers'it.

Thus the immediate effect of an increase of solar radiation would be an increase of evaporation. An addition of but 10° Fah. to the raean temperature of the earth's atmosphere would increase its capacity for vapour sufficiently to enable it to take above three inches more of water from the surface of the ocean and hold it as trans.

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