Читать книгу The Age of Wonder: How the Romantic Generation Discovered the Beauty and Terror of Science - Richard Holmes - Страница 27

Once they had moved to Datchet, Herschel and his brother Alexander started an exclusive business in the manufacture of high-quality reflector telescopes. The first five of them, all seven-foot reflectors, were ordered by King George as royal gifts, and although never fully paid for by the Crown office (they were priced at a hundred guineas each), they had the invaluable effect of making Herschel the royal telescope-maker, ‘By Appointment’. All telescopes, whatever their size, were individually constructed to order, took three or four weeks to make, and had an individual price, usually quoted in guineas. Herschel would supply them either in kit form or fully assembled in beautiful mahogany cases, with spare mirrors and a selection of eyepieces. Although every one was handcrafted, his immense energy achieved something like mass-production. Over the next decade he made 200 mirrors for the popular seven-foot telescope, 150 for the ten-foot, and eighty for the big twenty-five-foot, although not all of these were sold.¹⁵⁵

Prices rose steadily. The renowned seven-foot telescope was usually sold in kit form for thirty guineas, but Herschel gradually raised even the kit price to a hundred guineas, the figure he quoted to the German astronomer Johann Bode in Berlin.¹⁵⁶ Eventually a twenty-foot in kit form sold for 600 guineas. The luxury ten-foot reflector, complete with polished mahogany case, patent adjustable stand, a selection of eyepieces and a spare mirror, cost a princely 1,500 guineas.¹⁵⁷ Indeed the more expensive models were sold mostly to German princes, and models also went to Lucien Bonaparte (Napoleon’s brother) and the Emperor of Austria.¹⁵⁸ Probably the most expensive commercial telescope that Herschel ever made was commissioned by the King of Spain for £3,500, and delivered to the Madrid Observatory in 1806.¹⁵⁹ Scores of Herschel’s telescopes were eventually sent all over England and Europe, and he personally delivered one on behalf of King George to the state observatory at Göttingen in 1786.¹⁶⁰

Gradually more and more visitors began to descend on the observatory at Datchet. Caroline started to keep a neat, double-columned visitors’ book, rather as if she were recording star observations, which in a sense she was. In spring 1784 the dying Dr Johnson sent the young Susannah Thrale (Mrs Thrale’s third daughter) on a visit, advising her to cultivate an acquaintance with Herschel: ‘He can show you in the night sky what no man before has ever seen, by some wonderful improvements he has made in the telescope. What he has to show is indeed a long way off, and perhaps concerns us little, but all truth is valuable and all knowledge pleasing in its first effects, and may subsequently be useful.’¹⁶¹

Caroline wrote vivid accounts of their routine of all-night star observations, or ‘sweeps’.¹⁶² Herschel’s technique of ‘sweeping’ did not-as the term seems to imply-involve moving the telescope laterally, which was always a tricky operation with the bigger reflectors. Instead it was kept on the meridian, and moved slowly up and down, while the constellations turned through the field of observation as the stars moved steadily across the night sky. As this motion is caused by the earth itself rotating on its polar axis, so the telescope is effectively ‘sweeping’ the heavens like some immensely long broom, or the finger of a searchlight. By this method Herschel could progressively cover the entire night sky in a series of small strips, each covering about two degrees of arc.¹⁶³ The technique was far more accurate than any other stellar observation that had ever been undertaken before in the history of astronomy. But it was also immensely slow and painstaking. A complete sweep could take several years to complete.

During this time Herschel became so familiar with every part of the sky that he could identify stellar patterns, and any new objects, with amazing speed and precision. Perhaps his musical training helped him here, as much as his painfully self-taught mathematics. As he suggested himself, he could read the night sky like a skilled musician sight-reading a musical score. Or more subtly, the brain that was trained to recognise the highly complex counterpoints and harmonies of Bach or Handel could instinctively recognise analogous stellar patternings.

Herschel became fascinated by both the physics and the psychology of the observation process itself, and later wrote some of his most fascinating papers about it. From 1782 he began to record the many physical tricks his eyes could play, and also began to study the illusions of night observation. On 13 November, while trying to identify a new double star in Orion, he dictated a careful note to Caroline:

Following 10 Orionii. I saw very distinctly double at least a dozen times pass through the whole field of view with both eyes, but was obliged to darken everything. I suspected my right eye to be tired, & know it to see objects darker. Therefore tried the left first, & saw it immediately pass thro’ the field double several times. Saw the same afterwards with the other eye…No star twinkled except Syrius, & those as low. The evening exceptionally fine for telescopes.¹⁶⁴

The more he was challenged by professional astronomers, the more Herschel became conscious of his ‘art of seeing’, and how it needed explaining afresh. ‘The eye is one of the most extraordinary Organs,’ he repeatedly told his correspondents. Classical physiology was wrong. Visual images did not simply fall upon the optic nerve, in the same sense that they fell upon a speculum mirror. The eye constantly interpreted what it saw, especially when using the higher powers of magnification. The astronomer had to learn to see, and with practice (as with a musical instrument) he could grow more skilful: ‘I remember a time when I could not see with a power beyond 200, with the same instrument which now gives me 460 so distinct that in fine weather I can wish for nothing more so. When you want to practise seeing (for believe me Sir,-to use a musical phrase-you must not expect to see at sight or a livre ouvert) apply a power something higher than what you can see well with, and go on increasing it after you have used it for some time.’¹⁶⁵

Caroline later assembled an index of all Herschel’s remarks on practical observation. Under ‘Trials of Different Eyes and Seeings’ she listed such topics as the distortion effect of ‘looking long at an object etc’, the need to progress from lower to higher powers of magnification, the fact that ‘different eyes judge differently of [the same] colours’, that ‘eyes tire’ without the observer noticing, and that ‘we see things always smaller at first, when difficult to be seen’.¹⁶⁶

Under another heading, ‘Airs and Situations’, she listed the particular locations and atmospheric conditions which affected a telescope. These were not always self-evident. The atmosphere itself had ‘prismatic powers’, and distortions could be produced by ‘field breezes’, viewing ‘over the roof of a house’, or standing ‘within 6 or 8 feet of a door’. Surprisingly, because of thermal ripples rising from the ground, ‘evenings tho’ apparently fine, are not always good for viewing’. By contrast, ‘moist air was favourable’, and damp or rain, even certain kinds of fog, were ‘no hindrance to seeing’. It was possible to observe in conditions of severe frost, or even falling snow, provided the mirrors were kept clear of ice.¹⁶⁷

Caroline gave the term ‘sweeping’ a certain domestic familiarity, so that in her letters she sometimes implies she is a sort of celestial housekeeper, brushing and dusting the stars to keep them in a good state for her brother, a sort of heavenly Hausfrau. But perhaps she also had deeper feelings about the cosmos she was now discovering. It was no longer a mere hobby to please him. Once they had moved to Datchet, in the summer of 1782 Herschel began to train her more carefully in observation techniques, so she could become a genuine ‘assistant-astronomer’. By way of encouragement he built her a special lightweight sweeper, consisting of ‘a tube with two glasses’ (i.e. a traditional refractor), and instructed her ‘to sweep for comets’.

Initially she found working on her own in the dark rather daunting. ‘I see from my Journal that I began August 22nd 1782, to write down and describe all remarkable appearance I saw in my sweeps, which were horizontal. But it was not till the last two months of the same year that I felt the least encouragement to spend the star-light nights on a grass-plot covered with dew or hoar frost, without a human being near enough to be within call.’¹⁶⁸ Besides, at this early stage Caroline knew ‘too little of the real heavens to be able to point out every object so as to find it again without losing too much time by consulting the Atlas’. As all novice astronomers find, stars move disconcertingly rapidly through a telescopic field of vision, even that of a low-powered telescope, and can easily slip away in the few moments spent consulting a star chart and then readjusting one’s eyes to night vision. (Night vision can take as long as thirty minutes to establish its full sensitivity.)

Clearly things were better for Caroline when Herschel was on hand in the garden, and not away at Windsor doing royal demonstrations. ‘All these troubles were removed when I knew my brother to be at no great distance making observations with his various instruments on double stars, planets etc, and I could have his assistance immediately when I found a nebula, or cluster of stars.’ In this first year Caroline found no comets, and only succeeded in identifying fourteen of the hundred or so known nebulae. She was too often interrupted by Herschel’s imperious shout, when he wanted her to write down some new observation made with the large twenty-foot.¹⁶⁹

Such teamwork was essential to the sweeping procedure that the Herschels developed. As William made his observations, he would call out precise descriptions of what he saw (with special attention to double stars, nebulae or comets). He would give magnitudes, colour and approximate distances and angles (using a micrometer) from other known stars within the field of view. Standing below him in the grass, and later sitting at a folding table, Caroline would meticulously note all this data down, using pen and ink and a carefully shrouded candle lantern, and consulting their ‘zone clock’ (a clock using a time scale related to the position of the stars, rather than the sun). Alexander Aubert would later give them a magnificent Shelton clock, with compensated brass pendulum, as a contribution to their work.¹⁷⁰

With Herschel, this was not tranquil or contemplative work, as might be supposed. Caroline would ‘run to the clocks, write down a memorandum, fetch and carry instruments, or measure the ground with poles etc etc of which something of the kind every moment would occur’.¹⁷¹ Sometimes she would call back questions, asking for further clarifications. Most importantly she would note the exact time of each observation, using the special zone clock, which would give a precise position as each object rotated through the meridian. By this method, at no point would William have to compromise his night vision by looking at a lit page and taking his own notes.

Herschel described their sweeping methods in a paper published in April 1786, ‘One Thousand New Nebulae’. Crucial to his technique was that he did not have to take his eye away from the lens, but could ‘shout out’ his observations while his assistant wrote them down and ‘loudly repeated’ them back to him. This had ‘the singular advantage’, as he put it, ‘that the descriptions were actually writing and repeating to me while I had the object before my eye, and could at pleasure correct them’. The distinct tone of military command was emphasised by the fact that nowhere in this paper did Herschel mention that his assistant was Caroline.¹⁷²

Standing under a night sky observing the stars can be one of the most romantic and sublime of all experiences.^♣ But the Herschels’ sweeps were fantastically prolonged and demanding. In clear weather, they would often go on for six or seven hours without a break. They began at eleven at night, and often did not go to bed before dawn, in a mixed state of exhaustion and euphoria. Both slept till midday, and the house had to be kept quiet most of the morning, although Caroline often seems to have been up early, drinking coffee and writing up the night’s observations in long, minute columns of figures: a sort of double book-keeping which she often referred to as ‘minding the heavens’.

Observations and note-making required dogged precision and absolute concentration. It could be chill even in summer, and in winter the frost covered the grass around them, and the wind moaned through the trees. (Nevil Maskelyne had a special woollen one-piece observation suit made for him at Greenwich, with padded panels that made him look like a premonition of the Michelin Man.) Herschel took to rubbing his face and hands with raw onions to keep out the cold. When Banks came down to join them he sometimes brought oversize shoes so he could wear half a dozen pairs of stockings inside them. Caroline layered herself in woollen petticoats. Frequently it was so cold that films of ice formed on the telescope mirrors, the ink clotted in the well, and frozen beads blunted the tip of Caroline’s quill.¹⁷³

It could also be dangerous. Caroline wrote: ‘I could give a pretty long list of accidents of which my Brother as well as myself narrowly escaped of proving fatal for observing with such large machineries, where all around is in darkness [and] is not unattended with danger; especially when personal safety is the last thing with which the mind is occupied at such times.’¹⁷⁴ The winter of 1783 was especially harsh. On one night in November that year, when William was mounted high up on the crossbar of his twenty-foot reflector, the wind almost blew him off, and when he hastily clambered down the rickety structure (’the ladders had not even the braces at the bottom’), the entire wooden frame collapsed around him; workmen had to be called to release him from the wreckage of spars.¹⁷⁵

On 31 December 1783, New Year’s Eve, over a foot of snow had fallen, and the sky was overcast. William however postponed celebrations, and insisted on the last sweep of the year. Caroline gives the impression that he was particularly impatient, and perhaps shouting at her more than usual. ‘About 10 o’clock a few stars became visible, and in the greatest hurry all was got ready for observing. My Brother at the front of the Telescope [was] directing me to make some alterations in the lateral motion.’ As she hurried round the base of the telescope, ‘having to run in the dark on ground covered foot deep in melting snow’, she slipped and tripped over a hidden wooden stake. These stakes were used to peg down the telescope frame with guy ropes, and had large iron hooks facing vertically upwards, ‘such as butchers use for hanging their joints on’.

Caroline painfully recounted what followed. ‘I fell on one of these hooks which entered my right leg about six inches above the knee. My brother’s call-make haste!-I could only answer by a pitiful cry-I am hooked!’ She was impaled, like a fish on a barb, and could not move. Herschel was still high up on the observation platform, in complete darkness, and did not immediately realise what had happened. It seems he continued to call down through the dark, ‘Make haste!’, while Caroline continued to gasp back in agony, ‘I am hooked!’¹⁷⁶

Finally he grasped the situation, and called for help from the assistant who had been adjusting the telescope frame. ‘He and the workman were instantly with me, but they could not lift me without leaving near 2 oz. of my flesh behind. The workman’s wife was called but was afraid to do anything.’ Caroline was carried back to the house, but astonishingly no doctor was called. She bandaged the wound herself, retired to bed, and proudly recorded that she was back on telescope duties within a fortnight. It seems that the extreme cold had an antiseptic effect on the large, open wound, and prevented fatal gangrene.

No doubt it was characteristic of Caroline to treat this wound lightly, and not make any fuss. Yet there is an uneasy sense throughout her account that William did not treat her with sufficient tenderness or care: ’I was obliged to be my own surgeon by applying acquabaseda and tying a kerchief about it for some days.’ The local Windsor physician, Dr James Lind, only heard about the accident a week later, ‘and brought me ointment and lint and told me how to use it’. The deep wound did not heal easily, but there is still no mention of William’s concern at any point. Eventually Dr Lind was called back to Datchet in early February 1784. ‘At the end of six weeks I began to have some fears about my poor Limb and had Dr Lind’s opinion, who on seeing the wound found it going on well; but said, if a soldier had met with such a hurt he would have been entitled to 6 weeks nursing in a hospital.’¹⁷⁷ It is curious that Dr Lind compared Caroline to someone in military service, and it is hard to overlook a certain note of reproach in his words.^♣

Caroline surely intended some irony when she added in the Memoir: ‘I had however the comfort to know that my Brother was no loser through this accident for the remainder of the night was cloudy and several nights afterwards afforded only a few short intervals favourable for sweeping, and until 16 January before there was any necessity for exposing myself for a whole night to the severity of the season.’

The wound had largely healed by the summer, but it would later return to give her chronic pain in old age. Her pitiful cry-‘I am hooked!’-is curiously symbolic of her relations with her brilliant, domineering brother at this period, at a time when he was obsessed by his astronomical ideas to the exclusion of all else. Including, it might seem, his sister’s well-being; although we have only her word for this.¹⁷⁸

It is hardly surprising that Herschel was a little distracted. In 1784 and 1785 he drew together his most radical ideas about the cosmos, and published two revolutionary papers in the Royal Society’s Philosophical Transactions. These completely transformed the commonly held idea of our solar system being surrounded by a stable dome of ‘fixt stars’, with a broad ‘galaxy’ or ‘via lactae’ (meaning a ‘path or stream of milk’) of smaller, largely unknown stars spilt across it, roughly from east to west. This was a celestial architecture or ‘construction’, inspired fundamentally by the idea of a sacred temple, which had existed from the time of the Babylonians and the Greeks, and had not seriously been challenged by Flamsteed or even by Newton.¹⁷⁹

‘An Investigation of the Construction of the Heavens’, published in June 1784, quietly set out to change this immemorial picture. It was based on all Herschel’s ceaseless telescope observations, relentlessly pursued with Caroline over two years, with his new twenty-foot reflector telescope. He had identified 466 new nebulae (four times the number recently confirmed by Messier), and for the first time suggested that many, if not all, of these must be huge independent star clusters or galaxies outside our own Milky Way.¹⁸⁰

This led him on to propose a separate, three-dimensional shape to the apparent flat ‘milk stream’ of the Milky Way. His proposal was based on his new method of ‘gauging’ the number of stars in any direction as seen from the earth, and then deducing from the different densities observed the likely shape of this galactic star cluster as it would be seen looking ‘inwards’ from another galaxy. This was a daring mixture of observation and speculation. Herschel’s first galactic diagram appeared like a curious oblong box or tilting parallelogram of stars.¹⁸¹ But his later calculations produced the now-familiar discus shape of the Milky Way, with its characteristic arms spinning out into space, and the slight bulge of stars at its centre.¹⁸² He was never sure where the solar system was located in the galaxy, and at one point observed that its overall shape was relative, depending on the view as seen by ‘the inhabitants of the nebulae of the present catalogue…according as their situation is more or less remote from ours‘.¹⁸³

In the second paper, called simply ‘On the Construction of the Heavens’ (1785), Herschel began to develop these ideas into a startling new ‘natural history’ of the universe. He opened by arguing that astronomy required a delicate balance of observation and speculation. ‘If we indulge a fanciful imagination and build worlds of our own…these will vanish like Cartesian vortices.’ On the other hand, merely ‘adding observation to observation’, without attempting to draw conclusions and explore ‘conjectural views’, would be equally self-defeating.¹⁸⁴

His own conjecture would be radical. The heavenly ‘construction’ was not something architecturally fixed by the Creator, but appeared to be constantly changing and even evolving, more like some enormous living organism. His telescopes seemed to show that all gaseous nebulae were actually ‘resolvable’ into stars. They were not amorphous zones of gas left over from the Creation. They were enormous star clusters scattered far beyond the Milky Way, and were dispersed throughout the universe as far as his telescopes could penetrate. The nebulae themselves were active. Their function seemed to be that of constantly forming new stars out of condensing gas, in a process of continuous creation. They were replacing stars which were lost.

Herschel found a memorable phrase for this astonishing speculation: ‘These clusters may be the Laboratories of the universe, if I may so express myself, wherein the most salutary remedies for the decay of the whole are prepared.’¹⁸⁵ He also pursued the possibility that some nebulae may be ‘island universes’ outside the Milky Way, thereby hugely increasing the sense of the actual size of the cosmos. Among these was the beautiful nebula in Andromeda, ‘faintly red’ at the centre. By 1785 his nebulae count had risen to well over 900. They appeared ‘equally extensive with that which we inhabit [the Milky Way]…yet all separate from each other by a very considerable distance’.¹⁸⁶ He picked out at least ten ‘compound nebulae’ which he considered larger and more developed than the Milky Way, and imagined the star-cluster view of our own galaxies from theirs. ‘The inhabitants of the planets that attend the stars that compose them must likewise perceive the same phenomena. For which reason they may also be called Milky Ways by way of distinction.’¹⁸⁷

As Kant had speculated, the cosmos might be infinite, whatever that might mean. Though Herschel’s estimates of cosmological distances were much too small by modern calculation, they were outlandishly, even terrifyingly, vast by contemporary standards. Beyond the visible parts of our own Milky Way, he estimated that a huge surrounding ‘vacancy’ of deep space existed, ‘not less than 6 or 8 thousand times the distance of Sirius’. He admitted that these were ‘very coarse estimates’. The implications seemed clear, though they were cautiously expressed in his paper: ‘This is amply sufficient to make our own nebula a detached one. It is true, that it would not be consistent confidently to affirm that we were an Island Universe unless we had actually found ourselves everywhere bounded by the ocean…A telescope with a much larger aperture than my present one [twelve inches], grasping together a greater quantity of light, and thereby enabling us to see further into space, will be the surest means of completing and establishing the argument.’¹⁸⁸

The dramatic implications of these ideas were soon picked up by journalists and popularisers. The following year Bonnycastle assessed the situation in the first edition of his Introduction to Astronomy: ‘Mr Herschel is of opinion that the starry heaven is replete with these nebulae, and that each of them is a distinct and separate system, independent of the rest. The Milky Way he supposes to be that particular nebula in which our sun is placed; and in order to account for the appearance it exhibits, he supposes its figure to be much more extended towards the apparent zone of illumination than in any other direction…These are certainly grand ideas, and whether true or not, do honour to the mind that conceived them.’¹⁸⁹

Also contained in Herschel’s revolutionary paper of 1785 were the seeds of a new, long-term project. He was planning the building of a monster forty-foot telescope, with a four-foot mirror. This would be the biggest and most powerful reflector in the world. With this he believed he could resolve once and for all the problem of the nebulae-whether they were other galaxies far beyond the Milky Way, or merely gas clouds within it. He would also have a better chance of establishing the true distance of the stars, through the measurement of stellar parallax. Above all he believed he would be able to understand how the stars were created, and whether the whole universe was changing or evolving according to some definite law or plan. Finally, he believed he might establish if there were observable signs of extraterrestrial life, a discovery which would have enormous impact on philosophical and even theological beliefs.

There was one other small, but revolutionary, departure in his 1785 paper. For the first time William Herschel carefully credited Caroline in print with a small ‘associate nebula’ in Andromeda. It was a previously unknown cluster ‘which my Sister discovered on August 27 1783 with a Newtonian 2 foot sweeper’. It was not in Messier’s annual catalogue La Connaissance des Temps, so this was Caroline Herschel’s first new addition to the universe.¹⁹⁰

^♣ Caroline eventually wrote out two versions of this memoir, the first in summer 1821, when she was seventy, and the second in 1840. She also destroyed two sections of the original record which she did not want read by other family members. A composite version was edited by her great-niece, Mrs John Herschel, and published by Murray in 1769. The manuscript still exists in the private collection of John Herschel-Shorland. The individual Memoirs have been meticulously published by Michael Hoskin, as Caroline Herschel’s Autobiographies (2003). William wrote a ‘Memorandum of my Life’ when he was nearly sixty, but this was a sort of professional CV for fellow scientists, comparatively short and characteristically reserved (Herschel, Scientific Papers 1, p.xiii). For full details see the Bibliography.

^♣ Three of William Herschel’s works are currently available on CD. They are his Oboe Concertos in C major and E-flat major, and his Chamber Symphony in F major (Newport Classics, Rhode Island, USA, 1995). They are notable for their light musical touch and fine, sprightly melodic lines, sometimes with a certain melancholy in the slower passages. The rapid, complex orchestration around the solo oboe in the concertos is handled with great confidence, and suggests Herschel’s ability to manage patterns and counterpoint. This was a conceptual skill which he seemed to transfer (visually) to the patterning of stars and constellations. He moved from earthly music to the music of the spheres.

^♣ A typical brass eighteenth-century orrery showed the sequence of six known planets: Mercury, Venus, Earth, Mars, Jupiter (with moons) and Saturn (with rings) orbiting around a central sun (sometimes operated by clockwork and illuminated by candles). Flamsteed showed all constellations-such as Herschel’s early favourites Orion, Andromeda and Taurus-against mythological engravings of their signs: the Hunter, the Goddess, the Bull. His Atlas Coelestis catalogued 3,000 stars; the modern Hubble telescope has identified some nineteen million. But the presentation of the night sky as a curved dome of mythological constellations is still quite usual, as for instance in the magnificently restored curved ceiling of Grand Central Station, New York.

^♣ The use of horse-dung moulds for casting metal mirrors continued well into the twentieth century, with the 101-inch mirror of the Mount Wilson telescope in California, cast in Paris in 1920 and eventually used by Edwin Hubble to confirm Herschel’s theories about the nature and distance of galaxies in 1922. See Gale Christianson, Edwin Hubble: Mariner of the Nebulae (1995). Precision was never easy to obtain: the mirror of the modern orbiting Hubble Space Telescope was found to be two micrometres too flat at the edges, an error which cost $1.5 billion to correct in 1992.

^♣ In describing the rebel angel’s enormous glowing shield, Milton contrives in Paradise Lost a beautiful reference to Galileo’s refractor telescope and the view he achieved of the moon.

…The broad circumference

Hung on his shoulders like the Moon, whose orb

Through optic glass the Tuscan artist views

At evening from the top of Fiesole.

Or in Val d’Arno, to descry new lands,

Rivers, or mountains in her spotty globe.

(Paradise Lost, Book I, lines 288-. See also Book III, lines 589-, and Book 5, 262-)

Milton here includes Galileo’s confirmation of an imperfect, ‘spotty’ globe, as described in his famous treatise The Starry Messenger (1610). His observations of rugged lunar mountains and irregular craters proved that not all celestial objects were perfect, and so the theologians were wrong about the nature of God’s creation (as well as about the movement of the earth around the sun). More subtly, Milton puts forward the notion of the moon as the earth’s cosmic shield, battered by many warlike blows from meteors. A modern poet might assign that task to Jupiter. As a young man Milton claimed to have met Galileo in 1638, during his tour of Italy, and discussed the new cosmology. ‘There it was that I found and visited the famous Galileo, grown old, a prisoner to the Inquisition, for thinking in astronomy otherwise than the Franciscan and Dominican licensers thought’-John Milton, Areopagitica (1644).

^♣ The Great Andromeda galaxy, now classified as M.31, is 2.8 billion light years away, part of the laconically named ‘Local Group’ of galaxies, which includes our Milky Way. The Orion nebula, M.42, hangs just below the three stars of Orion’s belt, and is a gaseous star-cluster within our own galaxy, a mere 1.6 thousand light years away, sometimes known as the Sword of Orion. The M. numbers were assigned by Herschel’s contemporary, the Parisian astronomer Charles Messier, in an annual publication known as La Connaissance des Temps. His catalogue for 1780 held sixty-eight deep-sky objects. No astronomer yet had the least idea of the enormous distances involved, so huge that they cannot be given in terms of conventional ‘length’ measurement at all, but either in terms of the distance covered by a moving pulse of light in one year (‘light years’), or else as a purely mathematical expression based on parallax and now given inelegantly as ‘parsecs’. One parsec is 3.6 light years, but this does not seem to help much. One interesting psychological side-effect of this is that the universe became less and less easy to imagine visually. Stephen Hawking has remarked, in A Brief History of Time (1988), that he always found it a positive hindrance to attempt to visualise cosmological values.

^♣ As with road directions, a diagram is a much better way to explain parallax than a written sentence. But it is interesting to try. Parallax is basically a trigonometrical calculation applied to the heavens. Stellar parallax is a calculation which is obtained by measuring the angle of a star from the earth, and then measuring it again after six months. The earth’s movement during that interval provides a long base line in space for triangulation. So the difference in the two angles of the same star (the parallax) after six months can be used in theory to calculate its distance. In fact single stars are so far away that they did not provide sufficient parallax to be measured with the techniques available at the time. Herschel thought that double stars might provide a more obvious parallax, by triangulating their movements against each other, as observed over six months from earth. In fact no sufficient parallax was observed until the nineteenth century, when Thomas Henderson measured the distance to the nearest star, Alpha Centauri, as 4.5 light years in 1832, and the German astronomer Friedrich Bessel measured the distance to 61 Cygni as 10.3 light years in 1838. As both published their results in 1838, there was a priority dispute. The first galactic distances were established by Edwin Hubble, using the celebrated ‘red-shift’ method in the 1920s. It is intriguing that towards the end of his career Hubble thought that ‘red-shift’ might be less reliable than he had originally supposed, and galactic distances are still an area of dispute, although the ‘age’ of the entire universe is currently agreed at 13.7 billion years. Andromeda, incidentally, is ‘blue-shifted’, and therefore approaching our Milky Way, with which it will eventually collide-or cohabit.

^♣ Young, in Night Thoughts, also imagined an infinitely distant planet with extraterrestrial inhabitants, as if it were some remote Pacific island, not unlike Tahiti perhaps:

Canst thou not figure it, an Isle, almost

Too small for notice in the Vast of being;

Severed by mighty Seas of unbuilt Space

From other Realms; from ample Continents

Of higher Life, where nobler Natives dwell.

(Edward Young, Night Thoughts on Life, Death and Immortality, 1742-45, ‘Night IX, and Last’)

^♣ This question bears on the whole nature of science history and biography. Michael Hoskin has suggested in his essay ‘On Writing the History of Modern Astronomy’ (1980) that most histories of science continue to be ‘uninterrupted chronicles’, which run along ‘handing out medals to those who “got it right”’. They ignore the history of error, so central to the scientific process, and fail to illuminate science as a ‘creative human activity’ which involves the whole personality and has a broad social context-Journal for the History of Astronomy 11 (1980). To this one might add that Romanticism introduced three important themes into science biography. First, the ‘Newton syndrome’, the notion of ‘scientific genius’, in which science is largely advanced by a small number of preternaturally gifted (and usually isolated) individuals. Second, the existence of the ‘Eureka moment’, in which great discoveries are made without warning (or much preparation) in a sudden, blazing instant of revelation and synthesis. Third, the ‘Frankenstein nightmare’, in which all scientific progress is really a disguised form of destruction. See Thomas Söderqvist (ed.), The Poetics of Scientific Biography (2007).

^♣ The naming of the new planet was much disputed, and was not generally agreed until the mid-nineteenth century. Johann Bode, the editor of the authoritative Berlin Astronomical Yearbook, which quickly popularised the name ‘Uranus’, urged that a single name from classical mythology, with no national overtones, was required. With impeccable Prussian logic he pointed out that in Greek mythology Saturn (Kronos) was the father of Jupiter (Zeus), and Uranus (the Greek sky god) was the father of Saturn. It is so recorded in his great Uranographia (1801), which became the most influential celestial atlas of the early nineteenth century, replacing Flamsteed’s and cataloguing some 15,000 naked-eye stars.

^♣ It was also the first planet that was not easily visible and distinctive to the naked human eye (by colour, shape or position), and indeed it is quite frustrating to attempt to find with modern binoculars. Its presence was therefore curiously remote and mysterious, emphasising the largeness and strangeness of the new solar system (now doubled in size), but also breaking up the old, affectionate feeling for a much-loved planetary family. It is arguable that Uranus has still not fully entered into the popular mythology of the solar system, a difficulty not helped by the awkward pronunciation of its name in English, which worked better when given to the metal uranium in 1789. Herschel’s son John tried to remedy this by giving Uranus’s-try saying that!-two moons the feathery Shakespearean names of Titania and Oberon, from A Midsummer Night’s Dream.

^♣ The Botanic Garden was the best-selling long poem in English throughout the 1790s, after which its popularity suddenly declined, probably because its science was thought to be too materialist and ‘French’. It was the first poem which presented itself in terms of a moving, ‘photographic’ image of the world: ‘Gentle Reader…Here a Camera Obscura is presented to thy view, in which are lights and shade dancing on a white canvas, and magnified into apparent life!-if thou art perfectly at leisure for such trivial amusement, walk in and view the WONDERS of my ENCHANTED GARDEN.’ Darwin’s ‘antique’ prose style in this Prologue was an ironic foil to the dense, plain, highly informative manner of his scientific footnotes. Together these notes added up to a remarkable survey of the current state of the physical sciences in 1790.

^♣ Moon and star imagery recurs in Coleridge’s poetry throughout his life. One of his earliest known poems, ‘To the Autumnal Moon’, was a sonnet written at the age of sixteen from the lead rooftop of his London school. Many of his great West Country poems, such as ‘Frost at Midnight’ (1798), may be said to be suffused with moonlight. Greta Hall, where Coleridge lived at Keswick, was an old observatory, and from its leads he frequently recorded the state of moon, stars and the night sky, as well as his own little boy Hartley’s comments on them. His famous poem ‘Dejection’ (1802) begins with the image of the ‘winter-bright’ new moon, with ‘the old Moon in her lap’, presaging a storm. When later living alone at Malta, he used a naval telescope to observe the moon and stars, and wrote many notebook entries about his inexplicable instinct to worship the moon (1805). Even such a late poem as ‘Limbo’, probably written at Highgate, dramatises himself as an old man gazing up at the moon in a garden. He is blind-‘a statue hath such eyes’-yet mysteriously he can still sense the moonlight pouring down on him like a benediction: