The Age of Wonder: How the Romantic Generation Discovered the Beauty and Terror of Science

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.