Double tails of comets; comets of 1823, 1850, and 1851–Tails multiple, fan-shaped, rectilinear, curved–Variable number of tails belonging to the same comet; comets of Donati, of 1861 and of Chéseaux.

Generally a comet has but one tail, which varies considerably in form or size, or, at all events, appears to do so. Sometimes these changes take place very rapidly, but still, as a rule, the tail consists of one luminous train. Nevertheless, examples may be adduced of double and even multiple tails. The comets of 1807 and 1843 were furnished with double tails, or, what comes to the same thing, single tails formed of two branches of very unequal length. It was the same with the comet of 1823, about which Arago gives the following details:–

‘On the 23rd of January, 1824, the comet, in addition to its ordinary tail opposite to the sun, had another which was directed towards the sun, so that it resembled somewhat the great nebula of Andromeda. The first tail appeared to include a space of about 5°, but the length of the second was scarcely 4°. Their axes formed between them a very obtuse angle of nearly 180° (fig. 25). In the close vicinity of the comet the new tail was hardly to be seen. Its maximum brightness occurred at a distance of 2° from the nucleus. During the first few days in February the tail opposite to the sun wasalone visible ; the other had disappeared, or had become sofaint that the best telescopes in the clearest weather failed toshow any trace of it.’

Theory of the formation and development of cometary atmospheres under the influence of gravitation and a repulsive force–Calculations of M. Edouard Roche– Masses of the comets of Donati and Encke as determined by this method.

We are now about to see the same question, when investigated by another method, lead to results quite different to those of M. Babinet. Between the opinions–entirely conjectural, be it observed–of the savants of the eighteenth century who held that comets were bodies dense and massive as the planets, and those of some contemporary astronomers who regard them as visible nonentities, there is room for a determination which is removed from both extremes, and is moreover better justified.

For this method of determination we are indebted to M. Edouard Roche, professor in the Faculty of Sciences at Montpellier. In a series of very remarkable researches into the theory of cometary phenomena, which we shall analyse further on, M. Roche shows that there is a determinate relation between the distance of the comet from the sun, its mass, and the diameter of the portion of its nebulosity subject to the attraction of the nucleus, otherwise called the diameter of its true atmosphere. This relation holds at distances so remote from the sun that the repulsive force, either apparent or real which engenders the tail may be neglected.

We have seen what the telescope has taught us of the structure of comets, so complex and wonderfully mobile, so different in this respect from that of the planets or the sun. On the one hand we see solid or liquid bodies, bearing the most striking analogy to the terrestrial globe, surrounded like it by atmospheres of comparatively small extent, stable in every portion ; these are the planets, the moon, and the satellites of the planets. As regards the sun and the stars–which shine, like the sun, by their own light, and are, like him, as everything leads us to suppose, foci of light and heat to other planetary groups–if these bodies are incandescent gaseous masses, their condensation is so enormous and their physical constitution is comparatively so stable, that the changes of which they are perpetually the theatre have no appreciable effect upon their equilibrium. In comparison with comets they are permanent stars ; while comets seem to be nothing more than clouds–wandering nebulae, to employ the expression of Laplace, who has but reproduced in a more happy form the term so happily applied by Xenophanes and Theon of Alexandria.

RETROSPECTION.

As we close the record of Miss Herschel's residence in England, we may pause for a moment to look back over the space she had traversed while following, with unvarying diligence and humility, the path her brother marked out for her, first in blessed hourly companionship, when she was as necessary in his home as in his library, or among his instruments; and latterly, when with saddened heart but unflagging determination she continued to work for him, but saw his domestic happiness pass into other keeping.

While they toiled together through those first ten years of ever-deepening interest and marvellous activity, during which the rapid juxtaposition of mirror-grinding, concerts, oratorios, music lessons, and frequent papers written for philosophical societies, almost takes the breath away as we read,—the brother had “abundant opportunity of learning how far he could trust to his companion's readiness, as well as capability, to accept of duties as utterly remote from all that her previous life had prepared her for as if he had asked her to accompany him on a pilgrimage to Mecca. And thus, of all of whom he had made trial, it was not the brilliant Jacob, nor the gifted Alexander, but the little quiet, home-bred Caroline, of whom nothing had been expected but to be up early and to do the work of the house, and to devote her leisure to knitting and sewing, in whom he found that steady devotion to a fixed purpose which he felt it was possible to link with his own.

Familiar to all as is the name this volume bears, it is not without hesitation that the following pages are given to the world. To subject the memorials of a deeply earnest life to the eyes of a generation overcrowded with books, raises a certain amount of diffidence.

Of Caroline Herschel herself most people will plead ignorance without feeling ashamed, and yet may we not assert that Caroline Herschel is well worth knowing.

Great men and great causes have always some helper of whom the outside world knows but little. There always is, and always has been, some human being in whose life their roots have been nourished. Sometimes these helpers have been men, sometimes they have been women, who have given themselves to help and to strengthen those called upon to be leaders and workers, inspiring them with courage, keeping faith in their own idea alive, in days of darkness,

These helpers and sustainers, men or women, have all the same quality in common—absolute devotion and unwavering faith in the individual or in the cause. Seeking nothing for themselves, thinking nothing of themselves, they have all an intense power of sympathy, a noble love of giving themselves for the service of others, which enables them to transfuse the force of their own personality into the object to which they dedicate their powers.

LIFE AFTER HER BROTHER'S MARRIAGE.

With the second volume of “Recollections” all connected narrative and detailed relation of daily events ceases, and for the ten years from 1788 to 1798 there is not even the journal, which, however, was resumed in the latter year. All has been destroyed. An event so important as her brother's marriage is only noticed as fixing the date when the “place of a housekeeper” had to be resigned. Miss Herschel lived from henceforth in lodgings, coming every day for her work, and in all respects continuing the same labours as her brother's assistant and secretary as before. But it is not to be supposed that a nature so strong and a heart so affectionate should accept the new state of things without much and bitter suffering. To resign the supreme place by her brother's side which she had filled for sixteen years with such hearty devotion could not be otherwise than painful in any case; but how much more so in this where equal devotion to the same pursuit must have made identity of interest and purpose as complete as it is rare. One who could both feel and express herself so strongly was not likely to fall into her new place without some outward expression of what it cost her—tradition confirms the assumption—and it is easy to understand how this long significant silence is due to the light of later wisdom and calmer judgment which counselled the destruction of all record of what was likely to be painful to survivors.

DIARY—continued—1810.

April 29th.—My nephew took leave of me, returning to Cambridge.

May 4th.—I went to Slough, my brother going to town with Mrs. H. He returned after a short stay, and I remained with him till Mrs. H. came home again. Some of my last days of staying at Slough I spent in papering and painting the rooms I was to occupy in a small house of my brother's attached to the Crown Inn, to which I removed.

July 13th.—I went to remain at my brother's house during the time he, with Mrs. H. and Miss Baldwin, went to Scotland.

Sept. 18th.—My brother and the family returned, and Dietrich came to Slough, a room being prepared for him in my cottage.

Dec. 1st.—Dietrich went to town to enter on his winter engagement.

July 22nd.—My brother with his family left Slough on a tour to Edinburgh and Glasgow. I went to his house till they returned, Sept. 18th.

SIR JOHN HERSCHEL AT THE CAPE.

Cape Town, Jan. 21, 1834.

My dear Aunt,—

Here we are safely landed and comfortably housed at the far end of Africa, and having secured the landing and final stowage of all the telescopes and other matters, as far as I can see, without the slightest injury, I lose no time in reporting to you our good success so far. M. and the children are, thank God, quite well; though, for fear you should think her too good a sailor, I ought to add that she continued sea-sick, at intervals, during the whole passage. We were nine weeks and two days at sea, during which period we experienced only one day of contrary wind. We had a brisk breeze “right aft” all the way from the Bay of Biscay (which we never entered) to the “calm latitudes,” that is to say, to the space about five or six degrees broad near the equator, where the trade winds cease, and where it is no unusual thing for a ship to lie becalmed for a month or six weeks, frying under a vertical sun. Such, however, was not our fate. We were detained only three or four days by the calms usual in that zone, but never quite still, or driven out of our course, and immediately on crossing “the line,” got a good breeze (the south-east trade wind), which carried us round Trinidad, then exchanged it for a northwest wind, which, with the exception of one day's squall from the south-east, carried us straight into Table Bay.

MISS HERSCHEL TO J. F. W. HERSCHEL.

Feb. 1, 1826.

My dearest Nephew,—

On the 17th January I received by the same post your letters of December 30th and January 9th. I should have answered your precious communication of December 30th immediately if I was not in hopes of receiving daily an answer to what I sent on the 28th December. I cannot express my thanks sufficiently to you for thinking me worthy of forming any judgment of your astronomical proceedings, and am only sorry that I cannot recall the health, eyesight, and vigor I was blessed with twenty or thirty years ago; for nothing else is wanting (and that is all) for my coming by the first steamboat to offer you the same assistance (when sweeping) as, by your father's instructions, I had been enabled to afford him. For an observer at your twenty-foot when sweeping wants nothing but a being that can and will execute his commands with the quickness of lightning [!], for you will have seen that in many sweeps six or twice six, &c., objects have been secured and described within the space of one minute of time.

I cannot think that any catalogue but the MS. one in zones (which was only intended for your own use) would facilitate the reviewing of the Nebulæ, and you are the only one to whom 1885, viz., 2nd and 3rd class, out of the 2500, can be visible in your twenty-foot.

LIFE OF THE BROTHER AND SISTER IN BATH.

At the time when William Herschel brought his sister back with him to Bath, he had established himself there as a teacher of music, numbering among his pupils many ladies of rank. He was also organist of the Octagon Chapel, and frequently composed anthems, chants, and whole services for the choir under his management. On the retirement of Mr. Linley (father of the celebrated singer, afterwards the beautiful Mrs. Sheridan) from the direction of the Public Concerts, he at once added this to his other avocations, and was consequently immersed in business of the most laborious and harassing kind during the whole of the Bath season. But he considered all this professional work only as the means to an end; devotion to music produced income and a certain degree of leisure, and these were becoming every day more imperatively necessary. Every spare moment of the day, and many hours stolen from the night, had long been devoted to the studies which were compelling, him to become himself an observer of the heavens. Insufficient mechanical means roused his inventive genius; and, as all the world knows, the mirror for the mighty forty-foot telescope was the crowning result. To his pupils he was known as not a music-master alone. Some ladies had lessons in astronomy from him, and, at the invitation of his friend Dr. Watson, he became a member of a philosophical society then recently started in Bath, to which he for several years contributed a great number of papers on various scientific subjects.

RECOLLECTIONS OF EARLY LIFE IN HANOVER.

Caroline Lucretia Herschel was born at Hanover on the 16th of March, 1750. She was the eighth child and fourth daughter of Isaac Herschel, by Anna Ilse Moritzen, to whom he was married in August, 1732. The family consisted of ten children, four of whom died in early childhood.

A memorandum in the handwriting of Isaac Herschel, transcribed by his daughter in the original German at the beginning of her Recollections, traces the family back to the early part of the seventeenth century, about which time, it appears that three brothers Herschel left Moravia on account of their religion (which was Protestant), and became possessors of land in Saxony. One of these brothers, Hans, was a brewer at Pirna, a little town two miles from Dresden, and the father of two sons, one of whom, Abraham by name, was born in 1651, was the father of the abovementioned Isaac, and the grandfather of Caroline Lucretia Herschel. Abraham Herschel was employed in the royal gardens at Dresden, he received commissions from various quarters on account of his taste and skill as a landscape gardener. Of his four children, Eusebius, the eldest, appears to have kept up little or no intercourse with his family after the father's death in 1718. The second child, Apollonia, married a landed proprietor, Herr von Thümer.