The dis- tance of the tree can be calculated when the base AB and the angles at A and B are known. Robert Hooke in the seventeenth century, and James Bradley in the eighteenth, both selecting the same star Gamma Draconis , looked for such a variation in its meridian altitude, but neither of them succeeded in establishing it, though Bradley was confident that had the parallax amounted to as much as one second of arc he would have detected it.
Upholders of the Copernican theory were somewhat embarrassed by such failures; but they could argue plausibly and, as the event proved, correctly that the stars were at such vast distances from us that their correspondingly minute parallaxes were too small to be detected with the instruments available.
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That was broadly the position when Herschel first directed his attention to the matter. The second problem in stellar astronomy under dis- cussion about the middle of the eighteenth century con- cerned the arrangement of the stars in space. The stars, as we saw, were formerly supposed to be attached like silver studs to a rotating crystalline sphere of which the observer occupied the centre.
This view of them was adopted by Aristotle and his medieval followers, and, as a conventional Fig. By the end of the sixteenth cen- tury, however, it had begun to be suspected that the stars, which differ so markedly in brightness, might be at different distances from us. They might be distributed in depth so as to occupy a layer of space having a definite thickness, or they might even form an assemblage ex- tending outwards from the Sun to infinite distances in all directions. The Italian philosopher and arch-heretic Giordano Bruno, writing about , pictured the stars as suns of which our Sun was a typical specimen , each travelling freely through space accompanied by its train of inhabited planets.
The stars do not appear uniformly scattered over the sphere of the heavens. Besides tending to form clusters here and there, they crowd towards the luminous belt of the night sky which we call the Milky Way or Galaxy, and which Galileo's telescope showed to consist, in fact, very largely of faint stars. Wright grasped the essential idea that the reason why the stars appear crowded together in the Milky Way is not that they are really concentrated into a ring, but that the region occupied by the stars extends farther in all directions in the plane of the Milky Way than in the directions perpendicular to it.
He supposed the Sun to occupy a roughly central position among the stars, which are scattered at random in 'a kind of regular Irregularity of Objects' , so that the Milky Way arose as an optical effect due to the observer's looking through a greater thickness of stars in some directions than in others, and to his having no sense of the different distances of the stars which his vision encountered and which he projected in- discriminately on to the background of the sky cf.
Wright conceived the stars as suns, each attended by a train of planets and comets controlled by its gravitational attraction which, however, did not extend to neighbouring stars and their systems; and he thought that the barely per- herschel's heritage. Wright's theory remained generally un- known to the astronomers of his day; but a short summary of his book, published in a Hamburg periodical, came to the notice of Immanuel Kant of Konigsberg, then in his late twenties and working as a private tutor, but later to be- come one of the greatest philosophers of all time. Kant never saw Wright's book, but he was inspired by it at second hand to elaborate his own theory of the constitution and evolution of celestial systems, which went far beyond the merely descriptive aim of the Durham astronomer.
Early in Alexander Wilson, the first Professor of Practical Astronomy at Glasgow University, found himself discussing with his son Patrick why the stars do not fall into one another under their mutual attractions. They sought to solve the problem by asking why the planets do not fall into the Sun.
Here the explanation evidently lay in the 'projectile forces' of the planets, which maintain them in 'periodical motion' about the luminary; and the stars may similarly be preserved from 'one universal ruin' by revolving about the centre of the 'Grand System of the Universe' as Alexander Wilson wrote in his anonymous Thoughts on General Gravitation etc. Wilson may have been acquainted with Wright's little-known work; but Herschel nowhere in his writings refers to Wright, though much of his early manhood was spent in Wright's countryside.
He acknowledged it in a note appended to the paper and in a letter to Wilson. To sum up, until the age of Herschel astronomers had concerned themselves almost exclusively with the motions, mutual relations, and surface features of the Sun and its family of planets and satellites.
The stars they had treated as mere geometrical points upon a conventional sphere, requiring only to have their positions catalogued and mapped with all needful accuracy so that they might serve as pointers for the measurement of time and as markers for defining the locations of the Sun, Moon, and planets. But now stellar astronomy was about to enter upon a new phase in which a star would be regarded as a physical object possessing individual characteristics of position, of motion, of intrinsic brightness constant or variable , and, in due course, of much else besides — as possessing, too, an evolutionary history and as associated with neighbour stars through a common origin and a parallel development.
Chapter 2 Herschel's Life Story In memoranda which he wrote down from time to time William Herschel placed on record the chief events of his early life, while the journals and memoirs of his sister Caroline, and surviving letters to and from the Herschels, serve to chronicle the astronomer's later years.
William Herschel could trace his ancestry back to the seventeenth century when his great-grandfather, Hans Herschel, kept a brewery at Pirna, a town in Saxony. The second son of Hans was Abraham, who worked as a landscape gardener near Magdeburg; and Abraham's third son, Isaac, became the father of the astronomer.
An uncertain glimpse of an older generation is afforded by letters which William Herschel received in and in from a distant cousin. These letters tell how three brothers named Herschel, persecuted for their Protestant faith, migrated from Moravia to settle in Saxony. One the writer's ancestor made his home at Schmilka, another in Postel- nitz, and the third from whom the astronomer was des- cended in Pirna. Isaac Herschel was born in He, too, worked for a time as a gardener; then he turned to music and, having learnt to play the oboe, he joined the band of the Hanoverian Foot-Guards.
They had ten children of whom six reached maturity. We shall be chiefly concerned in the following pages with the life and work of the second surviving son, Friederich Wilhelm, who was born in Hanover on 15 November and whom we shall henceforward call William Herschel, the name which he adopted when he settled in England and by which he was naturalized in Closely associated with him in his labours and in his fame was his younger sister, Caroline Lucretia, born on 16 March ; brief mention will also be made of the astronomer's elder brother Jacob , and of his younger brothers Alexander and Dietrich The children received their early education at the Garrison School; but they were given further instruction by their father, who also introduced them to astronomy.
William Herschel later recorded how 'my father's great attachment to music determined him to endeavour to make all his sons complete musicians, and. And from Caroline we have the reminiscence: 'My father was a great admirer of astronomy, and had some knowledge of that science; for I remember his taking me, on a clear frosty night, into the street, to make me ac- quainted with several of the most beautiful constellations, after we had been gazing at a comet which was then visible.
And I well remember with what delight he used to assist my brother William in his various contrivances in the pursuit of his philosophical [scientific] studies' Memoir and Correspondence of Caroline Herschel, 7f. The months of garrison duty were spent in Kent, where William found time to learn English; and the Herschels were received into local musical circles, making friends who were to be of great assistance to the two brothers when, a year later, they returned to England to seek their fortunes.
Jacob now obtained his discharge and returned home; and by the end of the year the whole regiment was back in Hanover. In the spring of the Foot-Guards were involved in a campaign against the French, an episode in the Seven Years War, which ended disastrously for the Hanoverians at the battle of Hastenbeck, William and his father sharing the hardships of the fighting-men.
William had joined the regimental band at so early an age that he had not been formally enlisted, and his father advised him to leave the service, undertaking to obtain his discharge from the commanding officer. A formal document has been pre- served: signed by General A. The French having occupied Hanover, William made for Hamburg; here he was joined by his brother Jacob, and late in the autumn of the two young men crossed to England and made their way to London. Meanwhile the Hanover- ian forces went into captivity; but two years later, in , the French were defeated at Minden, the prisoners were set free, and Isaac Herschel returned home in peace.
They also took part in concerts and stayed during the summer months with some of their Kentish acquaintances. In the autumn of Jacob re- turned to Hanover to become one of the Court musicians. William sped him on his way with all the funds that he could spare. He had begun to wonder whether his prospects would not be brighter in the provinces, where competition was less severe; and in he gladly accepted an appoint- ment as bandmaster of a regiment of militia of which the Earl of Darlington was Colonel and which was just then quartered at Richmond in Yorkshire.
Herschel, however, terminated this engagement in the following year to work as a free-lance musician at a succession of north-country centres — Newcastle, Pontefract, Leeds, and Halifax where he acted as organist after the settlement of a law- suit to remove the organ as a 'heathenish thing'.
He was now regularly composing music; and notes of his activities during the years spent in the north country record the completion of numerous 'symphonies' and other pieces and his appearance at concerts, which enhanced his fame. And when Herschel led an Edinburgh orchestra in a per- formance of some of his own works in a St Cecilia's Hall concert the earliest public concerts in Britain , the philo- sopher David Hume was present and later invited the young composer to dine with him.
In the spring of Herschel visited his family at Hanover; this was to be his last sight of his father, who died three years later. Despite the hardships of this precarious, wandering life, and the strain of incessant musical performance, teaching, and composing, Herschel pursued, during his early years in England, an ambitious course of self-education.
A pastel portrait by J. Russell, 17, Greek he soon abandoned as leading him too far from his favourite studies. He made profitable use of every moment of leisure; and his son, Sir John Herschel, could recall having often heard his father relate how once, when he had been reading on horseback, he found himself standing in front of the horse with the book in his hand, having been tossed over the animal's head. After nearly ten years of this unsettled existence, Herschel was appointed to be organist of the Octagon Chapel in Bath, the fashionable west-country health resort; he entered upon his duties there towards the end of He was free to supplement his salary with the fees of pupils and the proceeds of concerts; and by his annual in- come had risen to nearly four hundred pounds, a con- siderable sum in those days.
His three brothers paid him prolonged visits; and in he indulged in a Continental tour, visiting Paris and Nancy on his way to Hanover. When he reached home he found his sister Caroline keep- ing house for her ageing mother and her extravagant brother Jacob. A close bond of affection had always existed between William and his sister, who now, despite efforts at self-education, seemed in danger of settling down as a household drudge. William had already discussed with his brother Alexander the possibility of having her trained as a singer; and when, later in the summer, he returned from Hanover to Bath, he brought Caroline with him to keep house and to be launched upon a musical career.
She en- joyed, indeed, a brief springtime of success as a vocalist; but soon the task of helping to train her brother's choir curtailed her own hours of practice, and when, a little later, she followed him into the unfamiliar world of science, her cherished hope of an independent career faded for ever. Herschel later described his gradual progression from music to astronomy in a letter to the mathematician Charles - 22 CHAPTER TWO Huttoii: 'The theory of music being connected with mathe- matics had induced me very early to read in Germany all what had been written upon the subject of harmony; and when not long after my arrival in England the valuable book of Dr Smith's Harmonics came into my hands, I per- ceived my ignorance and had recourse to other authors for information, by which I was drawn on from one branch of mathematics to another' [Scientific Papers, I, xix.
Following the study of Robert Smith's Harmonics, he passed on to the same author's Opticks, which contains an illustrated section on descriptive astronomy; and he was thus stirred to examine the wonders of the heavens for himself with the aid of such instruments as also fell within the wide scope of Smith's manual.
HerschcTs earliest re- corded astronomical observations date from February ; they relate to the planet Venus and to an eclipse of the Moon. For nearly ten years yet astronomy remained for him a marginal hobby, to be cultivated only in time spared from his professional duties. In 1 his diary shows him still giving up to eight music lessons a day, while by night he observes the heavens 'with telescopes of my own construction'; by he has deliberately reduced the daily number of his scholars to not more than three or four; and in he records how 'some of them made me give them astronomical instead of musical lessons'.
Herschel's reference to his employment of home-made telescopes foreshadows what was to be one of the most remarkable achievements of his whole career, his fashion- ing of a multitude of magnificent instruments of higher quality and power than any known before or obtainable elsewhere in his lifetime.
An outline of his technical procedures must be deferred to a later chapter; but a few passages from Caroline Herschel's memoirs may serve to show how ruthlessly her brother sacrificed leisure, comfort, and the graces of home life to his consuming passion to see further into space than any man before him: But every leisure moment was eagerly snatched at for resum- ing some work which was in progress, without taking time for changing dress, and many a lace ruffle was torn or bespattered by molten pitch, etc.
For my time was so much taken up with copying music and practising, besides attendance on my brother when polishing, since, by way of keeping him alive, I was constantly obliged to feed him by putting the victuals by bits into his mouth. This was once the case when, in order to finish a seven foot mirror, he had not taken his hands from it for sixteen hours together.
In general he was never unemployed at meals, but was always at those times contriving or making drawings of whatever came in his mind. Caroline could recall how her brother 'used to retire to bed with a basin of milk or glass of water, and Smith's "Harmonics and Optics," Ferguson's "Astronomy", etc. After a few years Herschel grew tired of desultory celestial observations and began to apply himself to one of the outstanding problems which had long perplexed astro- nomers and to which we have already referred, that of con- firming from observations of carefully chosen stars the annual revolution of the Earth about the Sun, and of determining the distances of those stars from us.
This quest soon turned into a search for 'double stars', close stellar pairs believed to afford a sensitive test of the Earth's motion.
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Herschel's earliest explorations of the 24 CHAPTER TWO heavens were phased into three successive 'reviews', marked by a progressive improvement in the power of the instruments employed and by a corresponding extension of scope so as to include fainter and fainter stars. Herschel's second review was begun in August ; and one evening late in December of that year he was ob- serving the Moon with an 8-foot reflector and had found it convenient to set up the instrument in the street in front of his house, which had no garden.
A gentleman passing at the time asked permission to look through the telescope: it was granted, and the passer-by proved to be William Watson, son of the more celebrated Dr William Watson, physician and pioneer in electrical experiments. Both were Fellows of the Royal Society and both were later knighted. The younger Watson promptly enrolled Herschel as a member of the short-lived Philosophical Society of Bath, then in process of formation; and it was before that studious company that the astronomer read his earliest scientific papers, to the number of thirty-one in all.
They covered a wide range of subjects, some physical 'What becomes of Light? Watson rendered Herschel an im- portant service by communicating to the Royal Society several other papers, of astronomical interest, which the young amateur had presented to the Bath fraternity.
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It was, again, in the course of this second review of the heavens, carried out with a reflecting telescope of 7 feet focal length, that Herschel, on 13 March , made a discovery of a kind unprecedented in recorded human history, nothing less than the detection of a major planet of the solar system. For his discovery of the new planet, which in due course received the name of Uranus, the Royal Society in November awarded Herschel its Copley Medal; and the following month he was elected a Fellow of the Society. In April Herschel was informed that King George III had expressed a wish to see him; and, having made out a list of double stars which could be shown to advantage, he packed his 7-foot telescope and travelled to London late in May.