The Age of Wonder (21 page)

8

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