menu_book Chapter 3

CHAPTER II. We now have to consider labors of a totally different character from those of Sir William Herschel. Exploration and discovery do not constitute the whole business of astronomy. The less adventurous, though not less arduous, task of gaining a more and more complete mastery over the problems immemorially presented to her may, on the contrary, be said to form her

primary duty. A knowledge of the movements of the heavenly bodies has, from the earliest times, been demanded by the urgent needs of mankind, and science finds its advantage, as in many cases it has taken its origin, in condescension to practical claims. Indeed, to bring such knowledge as near as possible to absolute precision has been defined by no mean authority as the true end of astronomy. Several causes concurred about the beginning of the last century to give a fresh and powerful

impulse to investigations having this end in view. The rapid progress of theory almost compelled a corresponding advance in observation. Instrumental improvements rendered such an advance possible. Herschel's discoveries quickened the public interest in celestial inquiries. Royal, imperial, and grand-ducal patronage widened the scope of individual effort. The heart of the new movement was in Germany. Here thereto the observatory of Flamsteed and Bradley had been the acknowledged

centre of practical astronomy. Greenwich observations were the standard of reference all over Europe, and the art of observing prospered in direct proportion to the fidelity with which Greenwich methods were imitated. Dr. Maskelyne, who had the post of astronomer royal during 46 years from 1765 to 1811, was no unworthy successor to the eminent men who had gone before him. His foundation of the nautical almanac in 1767 alone constitutes a valid title to fame. He introduced at the

observatory the important innovation of the systematic publication of results, and the careful and prolonged series of observations executed by him formed the basis of improved theories and corrected tables of the celestial movements, which were rapidly being brought to completion abroad. His catalogue of 36 fundamental stars was besides excellent in its way, and most serviceable. Yet he was devoid of Bradley's instinct for divining the needs of the future. He was fitted

rather to continue a tradition than to found a school. The old ways were dear to him, and indefatigable as he was, a definite purpose was wanting to compel him by its exigencies along the path of progress. Thus, for almost fifty years after Bradley's death, the acquisition of a small acromat, footnote 59, fitted to the old transit instrument, July 11, 1772, was the only notable change made in the instrumental equipment of the observatory. The transit, the zenith sector,

and the mural quadrant with which Bradley had done his incomparable work retained their places long after they had become deteriorated by time and obsolete by the progress of invention. It was not until the very close of his career that Maskelyne, compelled by Pond's detection of serious errors, ordered Troughton's Circle, which he did not live to employ. Meanwhile, the heavy national disasters with which Germany was overwhelmed in the early part of the 19th

century seemed to stimulate rather than impede the intellectual revival already for some years in progress there. Astronomy was among the first of the sciences to feel the new impulse. By the efforts of Bode, Olbers, Schroedinger, and Van Zach, just and elevated ideas on the subject were propagated, intelligence was diffused, and a firm ground prepared for common action in mutual sympathy and disinterested zeal. They received powerful aid through the foundation in 1804 by a young

artillery officer named von Rickenbach of an optical and mechanical institute at Munich. Here the work of English instrumental artists was for the first time rivaled and that of English opticians, when Fraunhofer entered the new establishment, far surpassed. The development given to the refracting telescope by this extraordinary man was indispensable to the progress of that fundamental part of astronomy which consists in the exact determination of

the places of the heavenly bodies. Reflectors are brilliant engines of discovery, but they lend themselves with difficulty to the prosaic work of measuring right ascensions and polar distances. A signal improvement in the art of making and working flint glass thus most opportunely coincided with the rise of a German school of scientific mechanisms to furnish the instrumental means needed for the reform which was at hand. Of the leader of that reform it is now time to

speak. Friedrich Wilhelm Bessel was born at Midden in Westphalia July 22, 1784. A certain taste for coupled with a still stronger distaste for the Latin accident directed his inclination and his father's choice toward a mercantile career. In his 15th year accordingly he entered the house of Kuhlenkamp and Sons in Bremen as an apprentice clock. He was now thrown completely on his own resources. From his father, a struggling government official, heavily weighted with a large family,

he was well aware that he had nothing to expect. His dormant faculties were roused by the necessity for self-dependence, and he set himself to push manfully forward along the path that lay before him. The post of supercargo on one of the trading expeditions sent from the Hanseatic towns to China and the East Indies was the aim of his boy's ambition, for the attainment of which he sought to qualify himself by the industrious acquisition of suitable and useful knowledge. He learned

English in two or three months, picked up Spanish with casual aid of a gunsmith's apprentice, studied the geography of distant lands which he hoped to visit, collected information as to their climates, inhabitants, products, and the courses of trade. He desired to add some acquaintance with the art, then much neglected, of taking observations at sea, and thus led on from navigation to astronomy, and from astronomy to mathematics. He groped his way into a new world.

It was characteristic of him that the practical problems of science should have attracted him before his mind was yet sufficiently matured to feel the charm of its abstract beauties. His first attempted observation was made with a sextant, rudely constructed under his own direction, and a common clock. Its object was the determination of the longitude of Bremen, and its success, he tells us himself, filled him with a rapture of delight which by confirming his tastes decided

his destiny. He now eagerly studied both Yerbach and von Sachs' Montelic correspondence, overcoming each difficulty as it arose with the aid of the Lands-Tratée d'Astronomie, and supplying with amazing rapidity his early deficiency in mathematical training. In two years he was able to attack a problem which would have tasked the patients, if not the skill, of the most experienced astronomer. Amongst the earl of Egremont's papers, von Sachs had discovered Harriot's observations on Halley's

comet at its appearance in 1607, and published them as supplement to Bode's annal. With an elaborate care inspired by his youthful ardour, though hardly merited by their loose nature, Bessel deduced from them an orbit for that celebrated body, and presented the work to Olbers, whose reputation in cometary researches gave a special fitness to the proffered homage. The benevolent physician-astronomer of Bremen welcomed with surprise delight such performance

emanating from such a source. Fifteen years previously the French Academy had crowned a similar work. Now its equal was produced by a youth of twenty, busily engaged in commercial pursuits, self-taught and obliged to snatch from sleep the hours to devote to study. The paper was immediately sent to von Sachs for publication, with a note from Olbers explaining the circumstances of its author, and the name of Bessel became the common property of learned Europe.

He had, however, as yet, no intention of adopting astronomy as his profession. For two years he continued to work in the counting house by day, and to pour over the mechanique celestand and the differential calculus by night. But the post of assistant in Schroeter's observatory at Lilienthal, having become vacant by the removal of Harding to Göttingen in 1805, Olbers procured an offer of it. It was not without a struggle that he resolved to exchange the desk for the telescope.

His reputation with his employers was of the highest. He had thoroughly mastered the details of the business, which his keen practical intelligence followed with lively interest. His years of apprenticeship were on the point of expiring, and an immediate and not unwelcome prospect of comparative affluence lay before him. The love of science, however, prevailed. He chose poverty and the stars, and went to Lilienthal with a salary of a hundred thalers

a year. Looking back over his life's work, Olbers long afterwards declared that the greatest service which he had rendered to astronomy was that of having discerned, directed, and promoted the genius of Bessel. For four years he continued in Schroeter's employment. At the end of that time, the Prussian government chose him to superintend the erection of a new observatory at Konigsberg, which after many vexatious delays caused by the prostrate condition of the country,

was finished toward the end of 1813. Konigsberg was the first really efficient German observatory. It became, moreover, a center of improvement, not for Germany alone, but for the whole astronomical world. During two and thirty years it was the scene of Bessel's labors, and Bessel's labors had for their aim the reconstruction on an amended and uniform plan of the entire science of observation. A knowledge of the places of the stars is the foundation of astronomy. Their configuration lends

to the skies their distinctive features, and marks out the shifting tracks of more mobile objects with relatively fixed and generally unvarying points of light. A more detailed and accurate acquaintance with the stellar multitude, regarded from a purely uranographical point of view, has accordingly formed at all times a primary object of celestial science, and was, during the last century, cultivated with zeal and success by which all previous efforts were dwarfed into

insignificance. In Le Land's Histoire Céleste, published in 1801, the places of no less than 47,390 stars were given, but in the rough, as it were, and consequently needing laborious processes of calculation to render them available for exact purposes. Piazzi set an example of improved methods of observation, resulting in the publication in 1803 and 1814 of two catalogs of about 7,600 stars, the second being a revision and enlargement of the first, which for their time

were models of what such work should be. Footnote 63. A new reduction of the observations upon which they were founded was undertaken in 1896 by Herman S. Davies of the U.S. Coast Survey. Stephen Groombridge at Blackheath was similarly and most beneficially active, but something more was needed than the diligence of individual observers. A systematic reform was called for, and it was this which Bessel undertook and carried through. Direct observation furnishes only what

has been called the raw material of the positions of the heavenly bodies. A number of highly complex corrections have to be applied before their mean can be disengaged from their apparent places on the sphere. Of these, the most considerable and familiar is atmospheric refraction, by which objects seem to stand higher in the sky than they in reality do, the effect being evanescent at the zenith and attaining, by gradations varying with conditions of pressure and temperature, a maximum

at the horizon. Moreover, the points to which measurements are referred to themselves in motion, either continually in one direction or periodically to and fro. The precession of the equinoxes is slowly progressive, or rather retrogressive, the nutation of the pole oscillary in a period of about 18 years, added to which the non-instantaneous transmission of light, combined with the movement of the Earth in its orbit, causes a small annual displacement known as aberration. Now it is easy

to see that any uncertainty in the application of these corrections saps the very foundations of exact astronomy. Extremely minute quantities, it is true, are concerned, but the life and progress of modern celestial science depends upon the sure recognition of extremely minute quantities. In these early years of the 19th century, however, no uniform system of reduction, so the complete correction of observational results is termed, had been established. Much was left to

the individual caprice of observers who selected for the several elements of reduction such values as seemed best to themselves. Hence arose much hurtful confusion, tending to hinder the united action and mar the usefulness of laborious researchers. For this state of things, Bessel, by the exercise of consummate diligence, sagacity, and patience, provided an entirely satisfactory remedy. His first step was an elaborate investigation of the precious series of

observations made by Bradley at Greenwich from 1750 until his death in 1762. The catalog of 3,222 stars which he extracted from them gave the earliest example of the systematic reduction on a uniform plan of such body of work. It is difficult, without entering into details out of place in a volume like the present, to convey an idea of the arduous nature of this task. It involved the formation of a theory of errors of each of Bradley's instruments and a difficult

and delicate inquiry into the true value of each correction to be applied before the entries in the Greenwich journals could be developed into a finished and authentic catalog. Although completed in 1813, it was not until five years later that the results appeared with the proud, but not inappropriate, title of Fundamenta Astronomia. The eminent value of the work consisted in this, that providing a mass of entirely reliable information as to the state of the heavens

at the epoch in 1755. It threw back the beginning of exact astronomy almost half a century. By comparison with Piazzi's catalogs, the amount of precession was more accurately determined. The proper motions of a considerable number of stars became known with certainty and definite prediction. The certificate of initiation into the secrets of nature at last became possible as regards the places of the stars. Bessel's final improvements in the methods of reduction were

published in 1830 in his tabula Regiomante. They not only constituted an advance in accuracy, but afforded a vast increase of facility in application and were at once and everywhere adopted. Thus astronomy became a truly universal science. Uncertainties and disparities were banished and observations made at all times and places rendered mutually comparable. More, however, yet remained to be done. In order to verify the greater strictness with the results

drawn from Bradley and Piazzi's catalogs, a third term of comparison was wanted, and this Bessel undertook to supply. By a course of 75,011 observations executed during the years in 1821-33, with the utmost nicety of care, the number of accurately known stars was brought up to above 50,000 and an ample store of trustworthy facts laid up for the use of future astronomers. In this department, Argalandr, whom he attracted from finance to astronomy and trained in his own

methods, was his assistant and successor. The great Bonder Musterung, in which 324,198 stars visible in the Northern Hemisphere are enumerated and the corresponding Atlas published in 1857-63, constituting a picture of our sidereal surroundings of heretofore unapproached completeness, may be justly said to owe their origin to Bessel's initiative and to form a sequel to what he commenced. But his activity was not solely occupied with the promotion of a comprehensive

reform in astronomy. It embraced special problems as well. The long-baffled search for a parallax of the fixed stars was resumed with fresh zeal as each mechanical or optical improvement held out fresh hopes of a successful issue. Illusory results abounded. Piazza, in 1805, perceived, as he supposed, considerable annual displacements in Vega, Aldebaran, Sirius, and Procyon, the truth being that his instruments were worn out with constant use and could no longer be

depended upon. His countrymen, Calandrielli, was similarly deluded. The celebrated controversy between Astronomer Royal and Dr. Brinkley, director of the Dublin College Observatory, turned on the same subject. Brinkley, who was in possession of a first-rate meridian circle, believed himself to have discovered relatively large parallaxes for four of the brightest stars. Pond, relying on the testimony of the Greenwich instruments, asserted their nullity. The dispute,

protracted for fourteen years from 1810 until 1824, was brought to no definite conclusion, but strong presumption on the negative side was abundantly justified in the event. There was good reason for incredulity in the matter of parallaxes. Announcements of their detection had become so frequent as to be discredited before they were disproved, and Struve, who investigated the subject at Dorpat in 1821, had clearly shown that quantities concerned were

too small to come within reliable measuring powers of any instrument then in use. Already, however, the means were being prepared of giving to those powers a large increase. On the 21st July, 1801, two old houses in an alley of Munich tumbled down, burying in their ruins the occupants, of whom one alone was extricated alive, though seriously injured. This was an orphan lad of fourteen named Joseph Fraunhofer.

The elector, Maximilian Joseph, was witness of the scene, became interested in the survivor, and consoled his misfortune with a present of eighteen ducats. Seldom was money better bestowed. Part of it went to buy books and a glass-polishing machine, with the help of which young Fraunhofer studied mathematics and optics, and secretly exercised himself in the shaping and finishing of lenses. The remainder of his purchase, his release from the tyranny of one

Weichelberger, a looking-glass maker by trade, to whom he had been bound apprentice on the death of his parents. A period of struggle and privation followed, during which, however, he rapidly extended his acquirements, and thus was eminently fitted for the task awaiting him, when in 1806 he entered the optical department of the establishment founded two years previously by von Rickenbach and Uten Schneider. He now zealously devoted himself to the improvement

of the achromatic telescope, and after a prolonged study of theory of lenses and many toilsome experiments in the manufacture of flint glass, he succeeded in perfecting December 12, 1817, an object glass of exquisite quality and finish, a nine and a half inches in diameter, and of fourteen feet focal length. This, as it was then considered, gigantic lens, was secured by strew for the Russian government, and the great doorpad refractor, the first of the large

achromatics which have played such an important part in modern astronomy, was, late in 1824, set up in the place which it still occupies. By ingenious improvements in mounting and fitting, it was adapted to the finest micrometrical work and thus offered unprecedented facilities, both for the examination of double stars, in which strew chiefly employed it, and for such subtle measurements as might serve to reveal or disprove the existence of a sensible stellar

parallax. Fraunhofer, moreover, constructed for the observatory at Konigsberg the first really available heliometer. The principle of this instrument, termed with more propriety a divided object glass micrometer, is the separation by a strictly measurable amount of two distant images of the same object. If a double star, for instance, be under examination, the two half lenses into which the object glass is divided are shifted until the upper star, say, in one image is brought into

coincidence with the lower star in the other, when their distance apart becomes known by the amount of motion employed. Footnote 68. The heads of the screws applied to move the halves of the object glass in the Konigsberg heliometer are of so considerable size that a thousandth part of a revolution, equivalent to one twentieth of a second of arc, can be measured with the utmost accuracy. This virtually new engine of research was delivered and mounted in 1829, three years

after the termination of the life of its divisor. The doorpad lens had brought Fraunhofer a title of nobility and the sole management of the Munich Optical Institute, completely separated since 1814 from the mechanical department. What he had achieved, however, was but a small part of what he meant to achieve. He saw before him the possibility of nearly quadrupling the light gathering capacity of the great acromat acquired by Struve. He meditated improvements in reflectors,

as important as those he had already affected in refractors, and was besides eagerly occupied with investigations into the nature of light, the momentous character of which we shall by and by have an opportunity of estimating. But his health was impaired, it is said, from the weakening effects of his early accident, combined with excessive and unwholesome toil, and still hoping for its restoration from a projected journey to Italy. He died of consumption June 7, 1826, aged 39 years.

His tomb in Munich bears the concise eulogy, E proxima vit sidira. Bessel had no sooner made himself acquainted with the exquisite defining powers of the Konigsberg Heliometer than he resolved to employ them in an attack upon the now secular problem of star distances. But it was not until 1837 that he found leisure to pursue the inquiry. In choosing his test star, he adopted a new principle. It had hitherto been assumed that our nearest neighbors in space must be found among

the brightest ornaments of our skies. The knowledge of stellar proper motions afforded by the critical comparison of recent with earlier star places suggested a different criterion of distance. It is impossible to escape from the conclusion that the apparently swiftest moving stars are, on the whole, also the nearest to us, however numerous the individual exceptions to the rule. Now, as early as 1792, Piazzi had noted as an indication of relative vicinity to the Earth,

the unusually large proper motion, 5.2 minutes annually of a double star, of the fifth magnitude in the constellation of the Swan. Still more emphatically, in 1812, Bessel drew the attention of the astronomers to the fact, and 61 Cygni became known as the flying star. The seeming rate of its flight, indeed, is of so leisurely a kind, that in a thousand years it will have shifted its place by less than three and a half lunar diameters, and that a quarter of

a million would be required to carry it round the entire circuit of the visible heavens. Nevertheless, it has few rivals in rapidity of movement, the apparent displacement of the vast majority of stars being, by comparison, almost insensible. This interesting, though inconspicuous object, then, was chosen by Bessel to be put to the question with his heliometer, while Stroub made a similar and somewhat earlier trial with the bright gem of Lyre,

whose Arabic title of the falling eagle survives as a time-worn remnant in Vega. Both astronomers agreed to use the differential method, for which their instruments, and the vicinity to their selected stars of minute, physically detached companions, offered special facilities. In the last month of 1838, Bessel made known the result of one year's observations, showing for 61 Cygni a parallax of about a third of a second, .3136 minutes.

Footnote 71. It should be explained that what is called the annual parallax of a star is only half its apparent displacement. In other words, it is the angle subtended at the distance of that particular star by the radius of the Earth's orbit. He then had his heliometer taken down and repaired, after which he resumed the inquiry and finally terminated a series of 402 measures in March 1840. The resulting parallax of .3483 minutes, corresponding to a distance about

600,000 times that of the Earth from the Sun, seemed to be ascertained beyond the possibility of Kvil, and is memorable as the first published instance of the fathom line, so industriously thrown into celestial space, having really an indubitably touched bottom. It was confirmed in 1842 through 43 with curious exactness by C.A.F. Peters at Polkawa, but later researchers show that it required increase to nearly half a second. Struve's measurements inspired less

confidence. They extended over three years, 1835 through 38, but were comparatively few and were frequently interrupted. The parallax, accordingly, of about a quarter of a second, .2613 minutes, which he derived from them for Alpha Lyra, and announced in 1840, has proved considerably too large. Footnote 75. Elkin's corrected result in 1897 for the parallax of Vega is .82 minutes. Meanwhile, a result of the same kind but a more striking character than either

vessels or struves had been obtained, one might almost say casually, by a different method and in a distant region. Thomas Henderson, originally an attorney's clerk in his native town of Dundee, had become known for his astronomical attainments and was appointed in 1831 to direct the recently completed observatory at the Cape of Good Hope. He began observing in April 1832, and the serious shortcomings of his instruments notwithstanding executed during the thirteen

months of his tenure of office a surprising amount of first-rate work. With a view to correcting the declination of the lustrous double star Alpha Centauri, which ranks after Sirius and Canopus as the third brightest orb in the heavens, he affected a number of successive determinations of its position, and on being informed of its very considerable proper motion, 3.6 minutes annually, he resolved to examine the observations already made for possible traces of paralytic displacement.

This was done on his return to Scotland, where he filled the office of astronomer royal from 1834 until his premature death in 1844. The result justified his expectations. From the declination measurements made at the Cape and duly reduced, a parallax of about one second of arc clearly emerged, diminished by Gill's and Elkin's observations, 1822 to 1883, to 0.75 minutes. But perhaps by an excess of caution, was withheld from publication until fuller certainty was

afforded by the concurrent testimony of Lieutenant Meadow's determinations of the same star's right ascension. When at last, January 9, 1839, Henderson communicated his discovery to the Astronomical Society, he could no longer claim the priority which was his due. Bessel had anticipated him with the parallax of 61 Cygni by just two months. Thus, from three different quarters, three successful and almost simultaneous assaults were delivered upon a long-beleaguered citadel of

celestial secrets. The same work has since been steadily pursued, with general results showing that as regards their overwhelming majority, the stars are far too remote to show even the slightest trace of optical shifting from the revolution of the Earth in its orbit. In nearly a hundred cases, however, small parallaxes have been determined, some certainly, that is within moderate limits of error, others more or less precariously. The list is an

instructive one in its omissions, no less than in its contents. It includes stars of many degrees of brightness, from Sirius down to a nameless telescopic star in the Great Bear. Yet the vicinity to Earth of this minute object is so much greater than that of the brilliant Vega. Of the brightest stars are found to have no sensible parallax, while the majority of those ascertained to be nearest the Earth are of fifth, sixth, or even ninth magnitudes. The obvious

conclusions follow that the range of variety and the sidereal system is enormously greater than had been supposed, and that estimates of distance based upon apparent magnitude must be wholly futile. Thus the splendid canopas, betegese, and Rigel can be inferred from their infinite remoteness to exceed our sun thousands of times in size and luster, while many inconspicuous objects, which prove to be in our relative vicinity, must be notably his inferiors. The limits of real stellar

magnitude are then set very widely apart. At the same time, the so-called optical and geometrical methods of relatively estimating star distances are both seen to have a foundation of fact, although so disguised by complicated relations as to be a very doubtful individual application. On the whole, the chances are in favor of the superior vicinity of a bright star over a faint one, and on the whole, the stars in swiftest apparent motion are among those whose actual

remoteness is least. Indeed, there is no escape from either conclusion, unless on a supposition of special arrangements in themselves highly improbable, and we may confidently say, non-existent. End of part one, chapter two.