God's glory in the heavens/Astronomy In America
Great Refractor, Cambridge Observatory, U.S.
XVII.
ASTRONOMY IN AMERICA.
It was with no little surprise that, on inquiry for Mr Alvan Clarke in Boston, we could hardly find a clue to his residence. America is proud of her great men, but the name of her great optician, familiar to every astronomer in Britain, was almost unknown in his own city. It was after considerable search that we found his residence and workshop in Cambridge, a suburb of Boston. Even in Cambridge it was difficult to find him. Boston, at the time, was loud in the praises of an opera-singer, a native of the city, who was on the eve of starting for England to exhibit her wonderful powers in London, and who afterwards drew forth the plaudits of the passengers in the steamer in which we crossed the Atlantic. There was no such celebrity accorded to the obscure worker in glass, who, with marvellous art and dexterity, was fashioning instruments to extend the limits of creation, and open up to view new worlds and systems. Yet, Mr Clarke was as proud of the limited circle that recognised his labours, as the opera-singer was of the applause of the crowd in the steamer or the theatre.
When we reached his neat villa, we were shewn to the rear, where stood his observatory and workshop, in a building precisely similar to an old Scottish keep, consisting of a square tower of several stories, with a single apartment in each. The middle story, reached by a ladder, was his reception-room, in which the lighter work was executed. The basement floor was devoted to the heavier and coarser work, and the highest was reserved for an observatory, in which a, beautiful equatorial was placed. We came in upon him at an inopportune moment. He was bent on being courteous, but he was evidently preoccupied with some grave care, which greatly perplexed him. The cause of his anxiety we soon found to be some tapping going on in the workshop below. Every successive blow seemed to intensify his apprehension, and the rebound of his feelings was something startling, when a voice from beneath sung out, "All's right." The tapping was the attempt of his son to detach the greatest lens in the world from the pitchbed, in which it was stuck fast for the purpose of grinding. A blow, in the slightest degree too strong, would be the destruction of the labour of many months, and the loss of some thousands of dollars. Now that the lens was safely detached, and the burden removed from his mind, Mr Clarke was free to pour out his genial nature, and exhibit the refreshing enthusiasm of a man whose heart is thoroughly in his work. He pointed with pride to a lens lying before him, the fellow of the one that had caused him so much anxiety. This was the great object of our curiosity, and well might a lover of lenses make a long pilgrimage to see such a sight. It is eighteen inches in diameter, a size far exceeding that of any existing telescope of value. The telescope in the Russian Observatory of Pulkowa, by Frauenhofer, and long considered the best in the world, is only fifteen inches. The great equatorial of Cambridge Observatory, connected with Harvard University, was executed by the successors of Frauenhofer in Munich, Merz and Mahler, and is believed to be somewhat superior, besides being one-eighth of an inch greater in diameter. This one-eighth enabled our Transatlantic friends to boast of having the largest existing achromatic telescope in the world. It was like a horse gaining a race by the fraction of a neck. Mr Clarke's lens distances all competitors, as its area is half as large again as that of the Cambridge equatorial. The glass was from Chance, Birmingham, and no defect could be traced in it. The figure and polish seemed also perfect, but the performance can never be confidently predicted before actual trial. The character of Mr Clarke as an optician, however, gives good ground for the belief that it will far surpass anything that has been yet attempted.
Telescopes, like guns, are rated according to their calibre. Everything depends on the size of the lens, all else being equal. The difficulty of obtaining good glass, and working the lens, increases enormously with the size. The rate is something like that of the speed of a steamer. Every successive knot per hour requires a rapidly increasing rate of expenditure of fuel; and every increase of the size of the object-glass implies a much higher proportion of trouble and expense. The difficulties increase so rapidly, that in the workshops even of Munich, nothing greater than fifteen inches would be attempted. All honour to the courageous attempt of Mr Clarke! The astronomical world will not grudge America this triumph. She has unexpectedly taken the lead in various departments of practical astronomy; and it will be somewhat singular if a self-taught artist should "beat the most skilful opticians of Europe.
The telescopes of Mr Clarke have been brought under the notice of English astronomers, chiefly through the Rev. Mr Dawes, one of our most reliable observers. He has made some important astronomical discoveries; and perhaps there is not a better judge of the performance of telescopes. The readers of the Notices of the Astronomical Society are familiar with the achievements of Mr Clarke's telescope in the hands of Mr Dawes. Admiral Smyth, another of our most laborious astronomers, bears ample testimony to the perfection in his art, acquired by the American optician. We have, then, good ground for hoping that this great telescope will mark another decided advance in astronomical discovery.
It may, at first sight, appear strange, that the object-glass of a refracting telescope cannot be made of great dimensions with as great facility as the metallic speculum of a reflecting telescope. The speculum of Lord Rosse's telescope is six feet in diameter; and yet this lens of Mr Clarke, though only eighteen inches, is regarded as one of monster dimensions. Apart from the working of the figure, there is this great difference, that, for the glass to perform well, it must be perfectly homogeneous throughout; while this is of no importance in the reflecting telescope. In the one case, the rays have to pass through the substance of the glass, and any inequality in its constitution produces distortion, or indistinctness in the image. If the glass is not perfectly homogeneous, the refraction is disturbed; but in the case of the reflecting telescope, the reflection is the same, however much the surface of the speculum may vary in density. This results from the law, that the angle of reflection is the same, whatever be the nature of the reflecting substance; while, in the case of refraction, the angle altogether depends on the nature of the refracting body. It is obvious, therefore, that if the lens be not homogeneous throughout, it will not possess that equality of action which perfect definition requires. But it is exceedingly difficult to obtain glass of large dimensions free from inequalities. It may be perfectly good to a cursory inspection, while, submitted to proper tests, it is wholly worthless for astronomical purposes. From this source of difficulty the reflecting telescope is entirely free, and, consequently, far greater dimensions may be attained.
The reflecting telescope, however, labours under the great disadvantage of being very cumbrous, as compared with a refracting telescope of the same power. A small refracting telescope, worked comfortably under the shelter of a dome, with nice adjustment and easy movements, usually performs more satisfactorily than reflectors, with lofty and unwieldy scaffolding, standing out of doors and the observers to the severities of the weather. The huge reflector is useful for occasional star-gazing, but the refracting telescope is the one always used for regular scientific observations; and the great aim of opticians is to improve the latter.
The length of Mr Clarke's telescope is small compared to the telescopes of former days. At the Observatory of Kew are the glasses of a telescope executed by Huygens. They belonged to the Philosophical Society, but the focal length being such as to require a tube as long as a tall church spire, they were never fitted up. Sometimes the glasses of such telescopes were used without a tube, the eye-glass being placed at an immense distance from the object-glass. The refracting telescope at once shrunk into small dimensions, at least in regard to length, as soon as the achromatic principle was applied by Dolland. The only way, previous to this, of obviating the defect of colour, was by making the focus very long; but Dolland, by simply making the object-glass compound, one part being of flint, the other of crownglass, dispensed with long tubes. An achromatic telescope of the present day, two feet in length, performs much better than one of Huygen's aerial telescopes 100 feet long. But while, for convenience, opticians try to make their telescopes as short as possible, they are struggling to expand in another direction, and to execute object-glasses as large as possible; and if three inches in advance of any other telescope be eflected, a great triumph will be gained. The astronomer has to enlarge his object-glass, precisely for the same reason that the owl expands its eye in the dark. The expanded eye does not magnify objects; it merely takes in more light, and sees more clearly. The mouse is large enough to be seen by the owl with contracted eye, but it is too indistinct to be visible; the pupil is therefore expanded, and the prey, though retaining the same apparent dimensions, is at once descried. So the astronomer often fails to descry objects, not because they are not large enough, but because they are not clear enough; and the only way of overcoming the difficulty, is by making his artificial pupil, namely, the object-glass, as large as possible.
M. Steinheil of Munich has, at last, succeeded in working lenses, according to the formula of Gauss, the effect of which will be to shorten greatly the length of telescopes. In the best achromatic telescopes, there is an outstanding aberration which cannot be compensated, and which increases with the size of the object-glass. To lessen the injurious effect, the telescope must be lengthened in a certain proportion, as the lens is- increased in size; but in M. Steinheil's plan, this proportion is much less than in ordinary telescopes. It is impossible to over-estimate the advantage of this in practical astronomy. Every advance in power is at present neutralised, in a great measure, by the cumbrous dimensions every increase in the size of the lens involves. The mere unwieldiness is a great drawback to accuracy, while it greatly increases the expense of fittings and buildings. The great refractors of the Pulkova and Cambridge Observatories weigh, with their machinery, about three tons each, and require expensive and cumbrous domes. An incalculable benefit would be conferred on science, if the same power could be obtained with half the length of tube.
In Mr Clarke's square keep we hoped to escape, for a little, from the tumult of war. The whole nation was stirred to its depths by the war feeling. Along the line of lake, river, and rail, there was nothing heard but the war-song, and loud notes of defiance. No one had patience to talk of anything but the war, and however people began, they ended always with the all-engrossing subject. In the Sabbath-school, the common school, the missionary meeting, the prayer-meeting, and even the church, their national and war-songs were sung. They might be omitted in the programme, but before the meeting closed, there was a demand for some exciting song. The refrain of the most popular one still sounded in one's ears, long after losing sight of the shores of America:—
"And the star-spangled banner in triumph shall wave
O'er the land of the free and the home of the brave."
The star-spangled banner floated from every spire and house-top, and waved in enormous folds from ropes stretched across the streets. The volunteers swarmed in every city, and many were already provided with very bright uniforms, the most popular being that of the Zouave. They were incessant in their demands for music, and what with the din of brass bands, and the boisterous demonstrations of undisciplined troops, the whole country was kept in an uproar. The very children, dressed in the Zouave costume, were let loose to beat their mimic drums in the street, or to charge with tiny bayonets the unwary guests in the corridors of the hotels; so completely was the whole population given up to the war excitement.
It was gratifying to find one man engaged in the peaceful pursuits of science; but even in Mr Clarke's sanctuary, the curse of war had cast its shadow. For, when allusion was made to the commercial aspect of his great undertaking, we found that we had touched upon a delicate subject. The great telescope was ordered by the University of Mississippi, and a munificent price was agreed upon; but the war banished all thoughts of telescopes, and of obligations of Southern to Northern States. This southern institution was ambitious of possessing by far the most powerful telescope in the world; but, by the stern exigencies of war, the money that was to be paid for this expensive toy must go to purchase bread and bullets.
The case of Mr Clarke is one of many illustrations that, in the grinding and polishing of lenses and specula, the amateur often surpasses the professional optician. Witness Sir William Herschel, who was a professional musician; Mr Ramage, who was a tanner in Aberdeen; Wx Lassels, who is a Liverpool merchant; Mr Nasmyth, an engineer; and, above all, Lord Rosse, who has carried the process of casting and polishing specula to such a pitch of refinement. Mr Clarke started in life as a printer, and afterwards took to portrait-painting, which he still practises to a certain extent, as a relaxation from his severer labours. It was not till he was upwards of forty years of age, that he turned his attention to telescopes. He was first attracted to the subject, by one of his boys asking his aid in casting a speculum for a small telescope, which he had taken a fancy to construct. From that time, the boy's amusement became the serious business of the father's life. What renders his success more remarkable is, that he, according to his own account, is totally unacquainted with mathematics. The signs of plus and minus are about the sum of his algebraical knowledge. How often does genius supersede what, to other men, would be an essential element to success! What sense is more essential to the student of natural history than that of sight; and yet Huber, one of the most successful and philosophic observers of modern times, was stone-blind! Mathematics, to the optician or astronomer, seem as essential as sight to the student of natural history; and, yet, some of the most popular writers on astronomy were totally destitute of the mathematical faculty. Ferguson could never understand the logical process by which the forty-seventh proposition of the first book of Euclid is proved; yet he perfectly understood the property of the right-angled triangle. He convinced himself of its truth by cutting the squares out on pasteboard, and weighing the largest one against the other two. The late Dr Dick, who did so much to diffuse a knowledge of the facts cf astronomy, never could master the logic of the pons asinorum, though he quite understood the nature of the property demonstrated. Mr Clarke is also a good example of his order in another respect. He is a hearty, hilarious man, like all amateur workers in lenses and specula, who are always overjoyed when they meet a brother who can enter into their tastes, and listen patiently to the detail of all their failures and successes. There is, certainly, something in the occupation that is calculated to bring out all that is genial and benevolent in a man's character. It was very satisfactory to hear Mr Clarke describe, in glowing terms, a late visit to England, when he made the acquaintance and enjoyed the hospitality of our English astronomers. The gratification, we doubt not, was mutual; and no English astronomer will pay a visit to the Cambridge optician without carrying away with him pleasant reminiscences of his home and his workshop.
Though America is now taking a lead in the manufacture of the optical part of telescopes, American astronomers freely admit that they are far behind in the mounting and graduation. By far the finest circles are executed in the workshops of Munich and London.
Not above half a mile from the workshop of Clarke, is the Cambridge Observatory, superintended by Bond the younger. We have already referred to the contributions of Bond the elder to astronomical science. He had the chief merit of inaugurating a new system of observing, which has quite revolutionised practical astronomy. We refer to what is called the American or Electro-recording plan; and our chief object in visiting the Observatory was to examine the details of the plan. America has the undisputed claim to the invention, which, if measured by its result, is one of the most important in modern astronomy. It is questionable, however, whether it should be rated very high, if measured by the inventive genius required. There are certain inventions, which, in the course of things, are inevitable; and it is a mere question of time when the fortunate parties will stumble upon them. For example, the application of electricity to the ringing of bells in large hotels, such as the Hôtel du Louvre in Paris, is a very obvious deduction from former applications, and no one would think it worth while to set up any claim to the invention. No doubt the application of electricity to astronomical observation was not so obvious as this. Still, it was clearly an application that must necessarily have been made in a short time. The Bev. Mr Ward Beecher, in an evening lecture in Brooklyn, which we had the pleasure of hearing, claimed the faculty of mechanical invention as the grand prerogative of the New England mind, and gave, as a proof, that if all the inventions in churns, and ploughs, and reapers were placed in a row, they would stretch from Maine to the Mississippi. But, granting this fertility of invention, would this long row of ingenious notions amount in value to a single invention with the stamp of genius? James Watt once remarked, that uneducated artisans sometimes stumble upon inventions in matters of detail, which may be of great practical value; but that almost never has such a man claimed the merit of an invention which involved some new principle not hitherto applied; and he took the governor of the steam-engine as an illustration. The application of centrifugal force to open and shut the throttle-valve has the stamp of genius; but the innumerable modifications of this principle have no such claim. It must be acknowledged, that if we take the higher class of inventions, America can claim but few contributions, notwithstanding the extreme ingenuity displayed in agricultural implements and domestic appliances.
There are several claimants of the invention, but, undoubtedly, Mr Bond has the chief merit in reducing it most successfully to practice. The improvement consists simply in this—that the sense of touch is substituted for that of hearing. In the former plan, you listened to the beat of a clock in the same room with the telescope, and the mind was strained in the attempt to tell the exact second, or even the tenth of a second, when a star passed across a wire. In the new plan the clock may be out of sight and hearing, and all you have to do is to press an ivory key the moment the transit is made 5 and, in another room, through the intervention of the electric current, the record is made. A pen, held as it were in the hand of the clock, marks the precise moment on a sheet of paper, drawn by machinery under the pen at an equable rate. While the machinery is in operation, the pen is marking off seconds by making lateral offsets on a straight line—the space between any two offsets being a second of time. The effect of pressing the key is to make an additional mark. This mark indicates the precise moment when the observation was made. Suppose a copy is given to a school-boy in which to write during the course of a certain hour, and that while writing he receives a nudge from his neighbour which blots his copy, the moment when this happened can be afterwards ascertained by marking the part of the page where the blot is found—this being on the supposition that the boy wrote at an equable rate during the hour. Now, the pen held in the hand of the clock writes at an equable rate, and when the observer presses the ivory key, which is equivalent to the nudge, it records the event by an additional mark, the precise instant of which may be ascertained to the hundredth of a second. On the wall of the recording room there was ranged a series of handles called switches, after the nomenclature of the railway. By moving these handles, you turned on the electricity to any particular instrument; so that every instrument in the establishment might he connected with the recording apparatus. The following figure shews the way in which the pen records
the time on the revolving barrel. It will be observed that the line traced by the pen is not continuous, but that it is broken by offsets, each of which marks a second of time. When an observation is taken, an additional and different offset is made by the pen, and it is only necessary to note the precise point in this broken line, where this offset is made, in order to determine the precise instant of observation. The intervals between the second's marks are sufficiently great, to enable an observation to be read off to the hundredth of a second.
In the dome was the great Frauenhofer telescope, alluded to as the best existing telescope. With the exception of the eighth of an inch in the diameter of the object-glass, it is precisely similar to the Pulkova telescope, the figure of which is familiar to every student of astronomy. The sight of the real instrument was like renewing acquaintance with an old friend. It was, however, with a species of reverence that one looked up to this monument of human genius, balanced on its massive pillar, and enshrined in its capacious dome. It was not the Bavarian artist you were inclined to do reverence to. No; he merely put the last stone on the pyramid which human genius had been rearing for ages. This telescope was the highest product of the human intellect; it was the combination of all sciences, for all had been laid under contribution to make a perfect instrument. In one point of view, man may well be proud of such an achievement; and, in another, how humbling is it! For what, after all, is its grand object? Is it not to teach us how little we do know? Man perched on the summit of the pyramid which his genius has reared, no doubt gets a somewhat wider range of view, but he has discovered only a little more of the fringe of the garment of the Omnipotent. No doubt the telescope unfolds new worlds and systems, but, after all, they are only the outer court of the temple of the Most High. The unknown only becomes more overwhelming, the more that we extend the limits of the known.
America is famed for her rocking-chairs, and all comfortable devices, but the perfection of comfort is the chair devised by Mr Bond, for observing with the great equatorial. The eye must follow the end of the telescope, which moves in a circle, and the chair must therefore move in a circle too, and so that you may be sometimes aloft in the dome, or sometimes down near the floor; and, besides all this, it must be moved to the right or left, at pleasure. Now, all these complicated movements can be executed without leaving your chair. By turning handles attached to the chair, you move up or down, along the concave of a circle, and to the right or left, at pleasure. All that you have to do is to observe at ease, and give an occasional pressure or tap with your finger. But may we not hope that the time is coming when it will not even be necessary for the astronomer to use his eyes? May he not construct an eye more reliable than his own, so that, in dealing with the stars, he will have only to expend the force of human intellect without any bodily exertion? Strange as it may appear, steps have been already taken to supersede the human eye. At Kew, the spots on the sun are daily recorded by an artificial eye, the object-glass forming the pupil, and a photographic plate the retina. This retina has the advantage over the human one of retaining the impression, so that precise measurements may be made at leisure.
At Dudley Observatory, in the outskirts of Albany, we found the director, Mr Mitchell, formerly of Cincinnati, in anything but a calm, scientific mood. and stars had lost their interest for the moment, and his thoughts were wholly of the war. He had returned, the morning we called, from Washington, where he had been summoned to give the benefit of his military skill, which has since raised him to the rank of Brigadier-General. He is one of the claimants of the invention of the electro-recording method of observation. His apparatus differs from Mr Bond's in this, that his sheet of paper is laid on a flat disc which turns round like the turn-table of a railway, while Mr Bond's is wound round a revolving cylinder. The most valuable instrument is a transit circle from Munich.
Miss Mitchell has gained an honourable distinction in astronomy by her discovery of comets. She was the first American, and the first lady, to receive the King of Denmark's gold medal for the discovery of comets. There is now so much competition in this line of research, that it requires a very quick eye and much patient observation to be first in the race.
It is creditable to the United States that so much has been done for astronomy, seeing that all has been done by private liberality. Both Cambridge and Dudley Observatories are entirely supported by subscription or mortified funds. The only exception is the Observatory of Washington, over which Commodore Maury presided up to the period of the Secession. He has cast in his lot with the Southern States, and has now abandoned his office. It is much to be regretted that the work of this National Observatory has been interrupted; as, from the competent staff of observers, some valuable results might be expected. It is to be hoped that peace will soon be restored, and that astronomical science will be cultivated with renewed ardour.
Besides the observatories above mentioned there are others at Yale College, Hudson, Ohio, Philadelphia, West Point, Georgetown, Cincinnati, Tuscaloosa (Alabama), Dartmouth College, Amherst College, and Chicago. Most of these, however, are of no service to science, as no provision has been made for the regular working of them. The popular interest is apt to exhaust itself in the purchase of instruments, which are soon entirely neglected, if a staff of observers is not appointed. Where proper provision has been made for observers, an abundant harvest of discovery and scientific fame has been reaped. The Observatory of Cambridge, alone, has entitled the United States to take rank, in astronomical science, with any European nation. The credit is all the greater, that the whole is due to private liberality and a generous appreciation of the wants of science. This institution was long contemplated, but some popular impulse was needed, and this was furnished by the great comet of 1843. As the sudden apparition of a bright star decided the astronomical career of Tycho Brahe, so this comet laid the foundation of Cambridge Observatory. In the case of the other observatories also, a comet or eclipse was generally required to stimulate the popular interest, and comets and eclipses are not useless, though they served no other purpose than to found observatories. Under the cometary influence, a meeting was held in Boston in 1843, and the sum of 20,000 dollars was subscribed on the spot for the Cambridge Observatory. One-half the sum was contributed by ten individuals; and of this half Mr David Sears gave 5000 dollars, to build a tower which now bears his name. The names of the munificent donors are, in a business-like manner, inscribed on a marble tablet, built into the internal wall of the dome. All honour to these liberal-minded merchants who have made their names historical by erecting 'this temple of science, destined alike to throw a lustre around their country, and proclaim the glory of God in the heavens.
It is unfortunate that, in British America, the taste for astronomy has not been caught up from the States. The people have not yet been trained to depend upon themselves for the advancement of such objects, and the Provincial Government have imitated the States in leaving science to struggle for itself. A step in advance, however, has at length been taken. The Government of Canada, along with the city of Kingston, have provided means for the erection of an observatory in connexion with the University of Kingston. It is to be hoped, that it will be so equipped and worked, as to maintain the credit of the British name in America, and extend the boundaries of astronomical science.