Edward S. Holden

“ In concluding this condensed account of Herschel's scientific labors, it behoves us to remember that there was nothing due to accident in his long life. He was born with the faculties which fitted him for the gigantic labors which he undertook, and he had the firm basis of energy and principle which kept him steadily to his work.
As a practical astronomer he remains without an equal. In profound philosophy he has few superiors. ”

“ If the sun alone had a motion, and the other stars were at rest, the consequence of this would be that all the fixed stars would appear to be retreating en masse from that point in the sky towards which we were moving. Those nearest us would move more rapidly, those more distant less so. And in the same way, the stars from which the solar system was receding would seem to be approaching each other. If the stars, instead of being quite at rest, as just supposed, had motions proper to themselves, then we should have a double complexity. ”

“ The simile is perfect, if we have the power to separate among the vast variety each state of being from every other, and if the very luxuriance of illustration in the heavens does not bewilder and overpower the mind. It was precisely this discriminating power that Herschel possessed in perfection. ”

“ We found him at his telescope. The comet was very small, and had nothing grand or striking in its appearance; but it is the first lady's comet, and I was very desirous to see it. Mr. Herschel then showed me some of his new discovered universes, with all the good humor with which he would have taken the same trouble for a brother or a sister astronomer; there is no possibility of admiring his genius more than his gentleness. ”

“ From 1786 until his death, Herschel remained at Slough; his life, truly speaking, was in his observatory.
It is indeed true, as Arago has said in his eloquent tribute to him: "On peut dire hardiment du jardin et de la petite maison de Slough, que c'est le lieu du monde où il a été fait le plus de découvertes. Le nom de ce village ne périra pas; les sciences le transmettront religieusement à nos derniers neveux." ”

“ They are attempts to gain a scale of celestial measures by which we may judge of the distances of the stars and clusters in which these changes are going on.
There is little to change in Herschel's statement of the general construction of the heavens. It is the groundwork upon which we have still to build. Every astronomical discovery and every physical fact well observed is material for the elaboration of its details or for the correction of some of its minor points. As a scientific conception it is perhaps the grandest that has ever entered into the human mind. ”

“ As a study of the height to which the efforts of one man may go, it is almost without a parallel. The philosopher who will add to it to-day, will have his facts and his methods ready to his hands. Herschel presents the almost unique example of an eager observer marshaling the multitude of single [Pg 213] instances, which he himself has laboriously gathered, into a compact and philosophic whole. In spite of minor errors and defects, his ideas of the nature of the sidereal universe have prevailed, and are to-day the unacknowledged basis of our every thought upon it. ”

“ It is clear that if in any given part of the sky, where, on the average, there are ten stars (say) to a field, we should find a certain small portion having 100 or more to a field, then, on Herschel's first hypothesis, rigorously interpreted, it would be necessary to suppose a spike-shaped protuberance directed from the earth, in order to explain [Pg 165] the increased number of stars. If many such places could be found, then the probability is great that this explanation is wrong. We should more rationally suppose some real inequality of star distribution here. ”

“ In his paper of 1792, Herschel shows that the most distant satellite of Saturn—Japetus—turns once on its axis in each revolution about its primary, just as our moon does. He says of this:
"I cannot help reflecting with some pleasure on the discovery of an analogy which shows that a certain uniform plan is carried on among the secondary planets of our solar system; and we may conjecture that probably most of the satellites are governed by the same law; especially if it be founded on such a construction of their figure as makes them more ponderous towards their primary planets." ”

“ The ratio of the light entering the eye when directed toward a star, to the whole light given out by the star, would be as the area of the pupil of the eye to the area of the whole sphere having the star as a centre and our distance from the star as a radius. [Pg 178] If the eye is assisted by a telescope, the ratio is quite different. In that case the ratio of the light which enters the eye to the whole light, would be as the area of the mirror or object-glass to the area of the whole sphere having the star as a centre and its distance as a radius. ”

“ If it is self-luminous, it seems more fit to produce a star by its condensation, than to depend upon the star for its own existence. Such were a few of the theorems to which his discovery of this nebula led him. The hypothesis of an elastic shining fluid existing in space, sometimes in connection with stars, sometimes distinct from them, was adopted and never abandoned. How well the spectroscope has confirmed this idea it is not necessary to say. We know the shining fluid does exist, and in late years we have seen the reverse of the process imagined by Herschel. ”

“ It is indeed true that unless a particular star is of the same intrinsic brightness as our largest stars, this reasoning does not apply to it; in just so far as the average star is less bright than the average brightness of our largest stars, will the numbers which Herschel obtained be diminished. But for every star of which his hypothesis is true, we may assert that his conclusions are true, and no one [Pg 176] can deny, with any show of reason, that, on the whole, his suppositions must be valid. On the whole, the stars which we call faint are farther from us than the brighter ones ”

“ If this be a true account of the solar heat, for the support of which I appeal to my experiments, it remains only for us to admit that such of the rays of the sun as have the refrangibility of those which are contained in the prismatic spectrum, by the construction of the organs of sight, are admitted under the appearance of light and colors, and that the rest, being stopped in the coats and humors of the eye, act on them, as they are known to do on all the other parts of our body, by occasioning a sensation of heat. ”

“ The question of determining the parallax of stars first brought Herschel to the discovery of double stars. If two stars, A and B, appear very close together, and if, in reality, the star B is very many times more distant from the earth than A, although seen along the same line of sight, then the revolution of the earth in its orbit will produce changes in the relative situation of A and B, and, in fact, B will describe a small orbit about A, due to this revolution. ”

“ If the stars are supposed all of the same absolute brightness, their brightness to the eye will depend only upon their distance from us. If we call the brightness of one of the fixed stars at the distance of Sirius, which may be used as the unity of distance, 1, then if it is moved to the distance 2, its apparent brightness will be one-fourth; if to the distance 3, one-ninth; if to the distance 4, one-sixteenth, and so on, the apparent brightness diminishing as the square of the distance increases. The distance may be taken as an order of magnitude. ”

“ Certainly, if Herschel's mind had been other than it was, the discovery of Uranus, which brought him honors from every scientific society in the world, and which gave him authority, might have had a hurtful effect. But, as he was, there was nothing which could have aided his career more than this startling discovery. It was needed for him. It completed the solar system far more by affording a free play to a profoundly philosophical [Pg 55] mind, than by occupying the vacant spaces beyond Saturn. ”

“ The quantity of this motion was not well known for any star when Herschel's researches began. Before they were concluded, however, Maskelyne had deduced the proper motions of thirty-six stars—the fundamental stars, so called—which included in their number Sirius, Procyon, Arcturus, and generally the brightest stars.
It is à priori evident that stars, in general, must have proper motions, when once we admit the universality of gravitation. That any fixed star should be entirely at rest would require that the attractions on all sides of it should be exactly balanced. ”

“ Every star will have its own appearance of a Galaxy or Milky Way, which will vary according to the situation of the star.
Such an explanation will account for the general appearances of the Milky Way and of the rest of the sky, supposing the stars equally or nearly equally distributed in space. On this supposition, the system must be deeper where the stars appear most numerous.
Herschel endeavored, in his early memoirs, to explain this inequality of distribution on the fundamental assumption that the stars were nearly equably distributed in space. ”

“ Of Herschel's discoveries, Arago thinks this has "le plus d'avenir." It may well be so. The laws which govern our solar system have been extended, through his researches, to regions of unknown distance. The binary stars will afford the largest field for research into the laws which govern them, and together [Pg 140] with the clusters and groups, they will give a firm basis by which to study the distribution of stars in general, since here we have the great advantage of knowing, if not the real distance of the two stars from the earth, at least that this distance is alike for both. ”

“ In the whole sky there are not above fifty such stars as the brighter of the two, and about four hundred of the brilliancy of B. These fifty and four hundred stars are scattered over the vault of heaven, almost at random. No law has yet been traced by which we can say that here or here there shall be a bright star like A, or a fainter one like B. In general the distribution appears to be fortuitous. How then can we account for one of the four hundred stars like B placed so close to one of the fifty like A? ”

“ William Watson, a Fellow of the Royal Society, distinguished for his researches in electricity, happened to see him at his telescope, and this led to a visit and an invitation to Herschel to join the Philosophical Society of Bath, then forming. This he gladly did, and it was of use to him in many ways.
He there formed acquaintance with men of his own way of thinking, and he himself became known. Better than all, he learned to [Pg 45] measure himself with other men, and by his early papers read to the Society, he gained skill in putting his thoughts before his hearers. ”

“ The whole field was open. What was perhaps more remarkable, there was in England, during Herschel's lifetime, no astronomer, public or private, whose talents, even as an observer, lay in the same direction.
It hardly need be said that as a philosopher in his science, he had then no rival, as he has had none since. His only associates even, were Michell and Wilson. [15]
Without depreciating the abilities of the astronomers of England, his cotemporaries, we may fairly say that Herschel stood a great man among a group of small ones. ”

“ One is almost ashamed to give space and currency to a forgotten attack, but it yields a kind of perspective; and it is instructive and perhaps useful to view Herschel's labors from all sides, even from wrong and envious ones. ”

“ The process consists simply in writing down the names of the stars, A, B, C, etc., in the order of their relative brightness. Thus if for a group of eight stars we have found at one [Pg 132] epoch A, B, C, D, E, F, G, H, and if at another time the order was A, B, C, D, F, E, G, H, symptoms of variability are pointed out. Repeated observations, where the same star is found in different sequences, will decide the question. Thus, for the stars visible to the naked eye, we know exactly the state of the sky in Herschel's day, now nearly a century ago. Any material change cannot escape us. ”

“ Here the essential peculiarities of the spectrum of each of the stars investigated by Herschel is pointed out, and if we were to use his observations alone to classify these stars into types, we should put Sirius and Procyon into one type of stars which have "all the colors" in their spectra; Arcturus and Aldebaran would represent another group of stars, with a deficiency of yellow and an excess of orange and red in the spectrum; and α Orionis would stand as a type of those stars with an excess of red and a deficiency of orange. ”

“ The Catalogue of Double Stars and the discovery of the Georgium Sidus, were the results of that review. The third was with the same instrument and aperture, but with a power of 460. This review extended to all the stars of Flamsteed's Catalogue, together with every small star about them, to the amount of a great many thousands of stars. I have, many a night, in the course of eleven or twelve hours of observation, carefully and singly examined not less than 400 celestial objects, besides taking measures, and sometimes viewing a particular star for half an hour together. ”

“ The planets Mercury, Venus, Mars, and Jupiter, although they were often studied, were not the subjects of his more important memoirs. The planet Saturn, on the contrary, seems never to have been lost sight of from the time of his first view of it in 1772.
The field of discovery always appears to be completely occupied until the advent of a great man, who, even by his way of putting old and familiar facts, shows the paths along which discoveries must come, if at all. ”

“ Moving the star to ten times its present distance would increase the surface of the sphere which it illuminates a hundred-fold. We cannot move any special star, but we can examine stars of all brightnesses, and thus (presumably) of all distances.
Herschel's argument was, then, as follows: Since with such a telescope one can see a star ten times as far off as is possible to the naked eye, this telescope has the power of penetrating into space ten times farther than the eye alone. ”

“ The data in the possession of the modern theorist is a thousand-fold that to be derived from Herschel's observations, and, while the subject of the internal construction of the sun is to-day unsettled, we know that many important, even fundamental, portions of his theory are untenable. A remark of his should be recorded, however, as it has played a great part in such theories:
"That the emission of light must waste the sun, is not a difficulty that can be opposed to our hypothesis. ”

“ If ever a series of observations was directed by profound and reasonable thought, it was Herschel's own.
"Dr. Herschel's passion for coining words and idioms has often struck us as a weakness wholly unworthy of him. The invention of a name is but a poor achievement for him who has discovered whole worlds. Why, for instance, do we hear him talking of the space-penetrating power of his instrument—a compound epithet and metaphor which he ought to have left to the poets, who, in some future age, shall acquire glory by celebrating his name. ”

“ Several stars of the first magnitude have been observed or suspected to have a proper motion; hence we may surmise that our sun, with all its planets and comets, may also have a motion towards some particular point of the heavens. . . . If this surmise should have any foundation, it will show itself in a series of some years in a kind of systematical parallax, or change, due to the motion of the whole solar system. ”

“ He returned to the subject of the revolution of stars about their axes again and again, and connected it with the revolution of satellites.
He found that the satellites of Jupiter and one of Saturn's periodically changed in brightness, and by quite simple means showed that their periods of rotation were at least approximately the same as their periods of revolution about their primaries. In this case, as in every other, he considered a discovery in each and every one of its possible bearings. There are no instances where he has singularly overlooked the consequences of his observations. ”

“ In the Philosophical Transactions for 1792, Schroeter had communicated a series of observations made with one of Herschel's own telescopes on the atmospheres of Venus, the Moon, etc. It was not only an account of phenomena which had been seen; it was accompanied by measures, and the computations based on these led to heights and dimensions for mountains on Venus which were, to say the least, extravagant. The adjective will not seem too strong when we say that the very existence of the mountains themselves is to-day more than doubtful. ”

“ It is perhaps probable that the hypothesis of equal brilliancy for all stars is still more erroneous than the hypothesis of equal distribution, and it may well be that there is a very large range indeed in the actual dimensions and in the intrinsic brilliancy of stars at the same order of distance from us, so that the tenth-magnitude stars, for example, may be scattered throughout the spheres which Herschel would assign to the seventh, eighth, ninth, tenth, eleventh, twelfth, and thirteenth magnitudes. ”

“ I have availed myself of the labors of preceding astronomers, but have been induced thereto by my own actual observation of the solar phenomena."
Herschel then refers to the theories advanced by his friend, Prof. Wilson, of Glasgow, in 1774. Wilson maintained that the spots were depressions below the sun's atmosphere, vast hollows as it were, at the bases of which the true surface of the sun could be seen.
The essence of his theory was the existence of two different kinds of matter in the sun: one solid and non-luminous—the nucleus—the other gaseous and incandescent—the atmosphere. ”

“ Since the stars of the Milky Way are permanently exposed to the action of a power whereby they are irresistibly drawn into groups, we may be certain that from mere clustering stars they will be gradually compressed, through successive stages of accumulation, till they come up to what may be called the ripening period of the globular form, and total insulation; from which it is evident that the Milky Way must be finally broken up and cease to be a stratum of scattered stars. ”