that they were by no means primarily directed to practical astronomy. Their effect in advancing the study of practical astronomy may be regarded as, in a sense, accidental; or rather this result affords an illustration of the fact that, in scientific research, we need not keep continually before our minds the question 'Cui bono?' since a good which the student of science himself cannot perceive will commonly result from even the least promising researches. We know that Copernicus only sought to explain observed appearances by a simpler theory than that which was in vogue in his day. To Kepler, perhaps, the idea may have suggested itself that the laws he sought for so earnestly, in order to explain the movements of Mars as traced by the best observational methods yet applied, might result in giving to astronomers a new power of predicting the motions of Mars and the other planets. But certainly the object which Kepler set himself was to replace the disorder of the Ptolemaic system and the but partial symmetry of the system of Copernicus, by a harmonious series of relations. When he had succeeded, his boast was, not that he had shown astronomers how thenceforth they might confidently predict the motions of the celestial bodies, but that he had 'found the golden vases of the Egyptians. Nor is it possible to Nor is it possible to read Newton's own account of those researches by which the law of gravitation was established without feeling that, to himself at least, the practical application of the law in aftertimes was of secondary import. It was the law itself, regarded as a discovery respecting the manner in which the bodies distributed throughout space influence and are influenced by each other, which he valued.

If we turn our thoughts to the astronomy of the past century, we recognise the same fact. It would

VOL. IV.-NO. XXI. NEW SERIES.

be difficult to find in the whole of that noble series of papers which Sir William Herschel contributed to the pages of the Philosophical Transactions a single paragraph directed to the application of astronomical discoveries to practical purposes. And whether we consider those discoveries which are commonly but erroneously supposed to constitute Herschel's chief title to honour, or those which astronomers regard as his most valuable contributions to science, we find in either case that we have to deal with discoveries which have, primarily, no practical value whatever. For example, the discovery of Uranus, which so many supposed to have been Herschel's noblest work, is undoubtedly full of interest, but it certainly was not a practically useful discovery. Nor, to turn to that which was in reality the noblest work achieved by Herschel-his researches into depths lying far beyond the range of the unaided vision-in what sense can the counting of myriads of stars or the discovery of thousands of nebula be regarded as advancing in the slightest degree the material interests of mankind? Even if it should hereafter happen that the discovery of Uranus or the processes of star-gauging may indirectly lead to some practical results of value, it would still remain certain that Sir William Herschel had had no such results in his thoughts when he prosecuted his researches.

In our own time Sir John Herschel has been justly held by all to be the leading astronomer of his day: yet it would be difficult to find in a single astronomical research of his the least practical value; while certainly in that long series of observations on which astronomers base their high opinion of him, there was no practical value whatever. Sir John Herschel had already devoted eight years of his life to the reexamination of his father's work

X

with the chief end of acquiring a mastery over his telescope, when at the Cape of Good Hope he began a series of observations which formed the exact counterpart of his father's observations in the northern skies. Star-gauging, the noting of double stars, the search for nebula -all these lines of research must needs advance the science of astronomy, but not one of them has any practical utility.

Nor, even if we take the wellmerited fame of departmental astronomers-if we may so distinguish the workers in special branches from men who, like the Herschels, have made all astronomy their subject can we recognise the title to such fame in practically useful work. When Adams and Leverrier by subtle processes of research showed astronomers where to turn their telescopes to detect the planet whose influence had disturbed the motions of Uranus, they were not in any way advancing the material interests of the human race. It may happen, indeed, that some of the mathematical processes devised or developed by these great men may one day be applied in some practical manner; but no one will, on this account, assign such practical results as the real title of Adams or Leverrier to astronomical fame. Even the practically useful work of such men as Hind and Airy is not that which is regarded among astronomers as affording their chief claim to honour. In future years Hind will be more spoken of as the discoverer of so many planetoids and the computer of such and such cometic orbits than as the skilful and successful superintendent of the Nautical Almanac; while Airy will be remembered rather as the discoverer of an inequality in the motion of Venus, and as the careful enquirer into the question of the sun's distance, than by reason of all those labours, great as is their commercial importance, which he has prosecuted or

superintended during his administration at Greenwich.

In considering astronomy as a subject of study, the first point to which we must direct our attention is the mode in which astronomical discoveries should be presented. I wish particularly to invite attention to the reasons of Sir John Herschel's great success in attracting the minds of men to a subject which, before his time, had been regarded as too recondite for general study. I wish to consider why it is that those facts which before his day seemed bewildering rather than impressive, became in his hands the means of attracting hundreds to the study of his favourite science. Herein I have to deal with the workings of my own mind; for, recalling my impressions of astronomical facts as presented by those works in which I first studied the science, and comparing those impressions with my feelings in regard to astronomy after I had read Sir John Herschel's Outlines of Astronomy, I find between my earlier and later views all the dif ference that exists between listlessness and earnestness.

The secret of Herschel's success I take to be the fact that he is never content with merely stating such and such circumstances about the celestial bodies, but will not leave his subject until he has impressed on the mind of his reader his own feeling of the reality of those circumstances. It would be easy to multiply examples of this characteristic peculiarity of his method of teaching; one, however, will suffice, and I take it almost at random:

He has described the actual relations of certain double stars; and so far as the facts respecting these objects are concerned, the reader has already had presented to him all that is necessary. Then, in that singularly effortless manner with which he always passes from description to imagery, he proceeds thus: It is not with the revolutions

of bodies of a planetary or cometary nature round a solar centre that we are now concerned-it is with that of sun round sun; each, perhaps, at least in some binary systems where the individuals are very remote and their period of revolution very long, accompanied with its train of planets and their satellites, closely shrouded from our view by the splendour of their respective suns, and crowded into a space bearing hardly a greater proportion to the enormous interval which separates them, than the distances of the satellites of our planets from their primaries bear to their distances from the sun itself. A less distinctly characterised subordination would be incompatible with the stability of their systems and with the planetary nature of their orbits. Unless closely nestled under the protecting wing of their immediate superior, the sweep of their other sun in its perihelion passage round their own might carry them off, or whirl them into orbits utterly incompatible with the conditions necessary for the existence of their inhabitants. It must be confessed that we have here a strangely wide and novel field for speculative excursions, and one which it is not easy to avoid luxuriating in.'

I have spoken of the absence of effort which characterises the introduction of such passages as these; and I take it that this absence of effort is absolutely essential to their effect. It is only when such passages are perfectly natural -natural not merely in appearance, but in reality-that they arouse the full sympathy of the reader. And their influence in this last respect might be taken as no unsafe test of their being purely natural effusions. But in the case of Sir John Herschel we have the means of proving, in an independent manner, that his most poetical descriptions were written, not to display his powers, but because they came

The

unbidden to his pen. We have the records of his observations as made in the stillness of night, with no thought but to represent what he had actually seen; and among these records we come again and again upon passages which no one familiar with Sir John Herschel's descriptive style could for a moment fail to recognise as his. Here, for example, are a few of his notes respecting the lesser Magellanic Cloud: they are taken from the Gaugebooks: 'The access to the Nubecula Minor is on all sides through a desert.' 'The lesser Nubecula is now approaching, but I discern no indications in the field leading me to expect any remarkable object: on the contrary, the stippled appearance noted shortly before is gone, and the ground is black. ground of the sky is completely black throughout the whole breadth of the sweep. The body of the cloud is fairly resolved into excessively minute stars, which, however, are certainly seen. It is a fine, rich, large cluster of very small stars, which fill more than many fields, and is broken into many knots, groups, and straggling branches, but the whole is clearly resolved.' Then, after passing the limits of the cloud, 'here is a region of utter barrenness-a miserably poor and barren region-most dreary since the small Nubecula.' Take also this sketch of a nebula, and the accompanying suggestion as to the constitution of certain regions of space, as affording evidence of the style of Herschel's note-books: A beautiful nebula; it has very much resemblance to the Nubecula Major itself as seen with the naked eye, but is far brighter and more impressive in its general aspect, as if the Nubecula were at least doubled in intensity. And who can say whether in this object, magnified and analysed by telescopes infinitely superior to what we now possess, there may not exist all the complexity

of detail that the Nubecula itself presents to our examination ?'

I believe that it is only by presenting astronomical facts in this striking and graphic manner that they can be made acceptable to the generality of readers. This is true, indeed, in all sciences; but it is specially true of astronomy, since there is no science where the facts are on the one hand so wonderful in reality, or on the other so capable of becoming unimpressive, and even wearisome, if not earnestly dealt with.

Yet let me in this place note that there is a fault of a different nature than want of earnestness, which equally requires to be avoided in scientific treatises. I refer to the undue familiarity of tone by which sometimes even our ablest expositors attempt to descend to the presumed level of their readers' comprehension. Even Sir John Herschel, it must be admitted, has sometimes condescended to express himself in too familiar terms when dealing with subjects which require grandeur of treatment. Not, indeed (so far as I remember), in his Outlines of Astronomy, at least in the main text of that noble work, but in some of his Essays, one is certainly somewhat startled at times by a familiarity which does not seem suited to the nature of the subject-matter. For example, I think that, without being hypercritical, the astronomer may fairly object to some points in the following passage, in which Sir John Herschel is speaking of the sun's attractive energy: Even in his capacity as ruler, the sun is not quite fixed. If he pulls the planets, they pull him and each other; but such family struggles affect him little. They amuse them' (the italics are not mine), and set them dancing rather oddly, but don't disturb him.' Nor again can one accept altogether with satisfaction that passage in which, after speaking of a comet as

of a restive horse, Herschel remarks, of the first three observations made on a comet, that the third nails it.'

The fact is that Sir John Herschel shows his real power as a scientific writer only when he deals grandly with grand subjects. Through this power he was unrivalled as a populariser of science. But in the less dignified rôle of a familiariser he was not successful. His gambolling was that of Behemoth. Nor, indeed, would his failure in this respect require notice, were it not that many have been led to follow his example in precisely that matter in which it was least desirable that he should be imitated. For instance, his fashion of calling the solar prominences 'things' by way of expressing their doubtful nature, has been followed as carefully as if it were an ornament rather than a blemish of his style. And one might readily cull from the writings of those who have imitated Herschel's familiar ity, passages which he assuredly would have shuddered at.

It is not merely necessary that astronomical facts should be so presented to the student that he may become possessed with a feeling of their reality, but the student cannot be rightly said to have astronomy' at all (to use Shakespeare's apt expression) until he is capable of picturing to himself, however inadequately, the truths of the science. A man may have at his fingers' ends the distances, volumes, densities, and so on of all the planets, the rates at which they move, the physical features they present, and a hundred other facts equally important; but, unless he has in his mind's eye a picture of the solar system, with all its wonderful variety, and all its yet more amazing vitality, he has not yet passed even the threshold of the science. He must be able to conceive the mighty mass of the sun