All these speculative essays assumed the high probability that extraterrestrial life existed, either within the immediate solar system, or further out among the stars. James Ferguson, for example, stated in the opening of his Astronomy Explained (1756) that the entire universe was evidently populated, if not positively crowded, with living forms: ‘Thousands upon thousands of Suns … attended by ten thousand times ten thousand Worlds … peopled with myriads of intelligent beings, formed for endless progression in perfection and felicity.’101 It was further assumed that such life forms, though not necessarily human in appearance, would have developed civilisations and sciences superior to our own. The question of whether they were ‘fallen’ in a religious sense, and required Redemption according to Christian doctrine, remained a moot point among astronomers, few of whom would have considered themselves as ‘atheists’ in any modern sense. ‘An undevout astronomer is mad,’ as the poet Edward Young reflected in Night Thoughts (1742-45).♣
However, the growing sense of the sheer scale of the universe, and the possibility that it had evolved over unimaginable time, and was in a process of continuous creation, did slowly give pause for thought. For a poet like Erasmus Darwin, in The Botanic Garden (1791), it put the Creator at an increasing shadowy distance from his Creation.102
This interest in extraterrestrial life was one of the reasons that Herschel remained so fascinated by the surface of the moon, with its mysterious mountains and craters, and dramatically shifting patterns and colours of shadow. When it was invitingly at the crescent (the best time to study surface detail), but too low to be observed from his tiny back yard, he would take his seven-foot telescope out into the cobbled street in front of the house. So it was, in December 1779, while Herschel was ‘engaged in a series of observations on the lunar mountains’, that a passing carriage stopped, a young gentleman sprang out, and he had his first historic meeting with Dr William Watson, junior. This was Herschel’s first really important scientific contact in England, one not made until he was forty-one. Watson was only thirty-three.
7
Herschel later recalled the moment with appropriate gravity: ‘The moon being in front of my house, late in the evening I brought my seven-foot reflector into the street … Whilst I was looking into the telescope, a gentleman coming by the place where I was stationed, stopped to look at the instrument. When I took my eye off the telescope, he very politely asked if he might be permitted to look in … and expressed great satisfaction at the view. Next morning, the gentleman, who proved to be Dr Watson, junior (now Sir William), called at my house to thank me for my civility in showing him the moon.’103
Caroline remembered it rather less formally. Herschel and Watson were so immediately taken with each other that very night that they burst into the house and began ‘a conversation which lasted until near morning; and from that time on [Dr] Watson never missed to be waiting on our house against the hours he knew my Brother to be disengaged’.104
Watson warmly befriended Herschel, and encouraged his work even to the extent of helping with pounding horse-dung moulds and casting speculum mirrors. He quickly became what Caroline called ‘almost an intimate of the family’.105 He had Herschel elected to the Bath Philosophical Society as ‘optical instrument maker and mathematician’ (no mention of musician), and over the next two years encouraged him to submit no fewer than thirty-one papers at its meetings. These included ‘On the Utility of Speculative Enquiries’, ‘On the Existence of Space’, and further unconventional observations on the moon. They are evidence of the extraordinary intellectual ferment that had seized upon Herschel.
His notion of the cosmos was already far from conventional, and several of these papers were what would now be called ‘thought experiments’. In his ‘Space’ paper, delivered on 12 May 1780, he astonished his audience with his radical thoughts on time and distance: ‘Huygens said that it was possible some of the fixt Stars might be so far off from us that their light tho’ it travelled ever since the Creation at the inconceivable rate of 12 million of miles per minute, was not yet arrived to us. The thought is noble and worthy of a Philosopher. But [should] we call this immense distance a mere imagination?. Can it be an abstract Idea?. Is there no such thing as space?’106
In the case of his moon speculations, he raises the question whether a scientific idea has to be ‘correct’ to be significant. One of Herschel’s most ingenious ideas was that moon craters were artificially constructed circular cities (or ‘Circuses’), built especially to harness solar power for the lunar inhabitants: ‘There is a reason to be assigned for circular Buildings on the Moon, which is that as the Atmosphere there is much rarer than ours and of consequence not so capable of refracting and (by means of clouds shining therein) reflecting the light of the Sun, it is natural enough to suppose that a Circus will remedy this deficiency. For in that shape of Building one half will have the direct, and the other half the reflected, light of the Sun. Perhaps, then on the Moon every town is one very large Circus?’107 ♣
So, besides the two main projects, to record all new double stars and all new nebulae, Herschel was also embarked on a third and partly secret programme in 1779: to discover life on the moon. For some time he did not risk sending this section of the lunar paper to Maskelyne at the Royal Society, but both Watson and Caroline were aware of it. This was one of the reasons he needed to construct better telescopes.
The moon project had begun with a long entry made in his Observation Journal for 28 May 1776. He saw ‘what I immediately took to be woods or large quantities of growing substances in the Moon’. With a certain angle of solar light, some of the lunar shadows looked like ‘black soil’ spread down a mountainside. Other puzzling stippled shadows, especially in the Mare Humorum, Herschel believed were enormous ‘forests’, made up of huge, spreading leafy canopies, or at least ‘large growing substances’. Because of low lunar gravity, this gigantic ‘vegetable Creation’ was evidently ‘of a much larger size on the Moon than it is here’.108
Similarly, he tended to believe that there were so many of the smaller moon craters that they must be artificial constructions: ‘By reflecting a little on this subject I am almost convinced that those numberless small Circuses we see on the Moon are the works of Lunarians and may be called their Towns.’ Nonetheless, true science required not speculation but accurate observation and telescopic proof. ‘But this is no easy undertaking to make out, and will require the observation of many a careful Astronomer and the most capital Instruments that can be had. However this is what I will begin.’109
The light-gathering power of Herschel’s seven-foot reflector allowed him to see many objects that no previous astronomers had accurately observed, or at least recorded. With Caroline taking notes at his dictation, they began to compose a new catalogue of double stars, and to develop a system of recording the exact time and position of any unusual stellar phenomena not previously catalogued by Flamsteed. By this means Herschel began to build up an extraordinary, instinctive familiarity with the patterning of the night sky, which gradually enabled him to ‘sight-read’ it as a musician reads a score. He would later himself use such musical analogies to explain the technique and art of observation.
In early 1781 it was decided to close down the millinery business at 5 Rivers Street. William and Caroline moved back to the substantial three-storey terraced house at 19 New King Street, where the telescope equipment was immediately set up in the fine little back garden: ‘beyond its walls all [was] open as far as the river Avon’. Here, as Caroline noted modestly, ‘many interesting discoveries were made’. At first she however had to remain at Rivers Street to oversee the selling off of the linen stock, and she missed the first few nights of observation in March. She subsequently recorded, with unusual care, that she did not return to New King Street until 21 March — as it turned out a historic absence.110
During these nights around the spring equinox Herschel was observing alone, and as well as continuing with their catalogue of double star
s, he gave himself up to making drawings of Mars and Saturn. Possibly he was ranging more freely than usual, or possibly he was testing his ability to ‘sight read’ the sky. At all events, on Tuesday, 13 March 1781, slightly before midnight, Herschel spotted a new and unidentified disc-like object moving through the constellation of Gemini. This discovery would change his entire career, and become one of the legends of Romantic science.
It also raises an intriguing question: how soon did Herschel know — or suspect — what he had discovered? It seems from his Observation Journal at the time, that what he thought he had found was a new comet. The following laconic account appears in his ‘First Observation Book’ for 12 and 13 March 1781
March 12
5.45 in the morning.
Mars seems to be all over bright but the air is so frosty & undulating that it is possible there may be spots without my being able to distinguish them.
5.53 I am pretty sure there is no spot on Mars.
The shadow of Saturn lays at the left upon the ring.
Tuesday March 13
Pollux is followed by 3 small stars at about 2’ and 3’ [minutes of arc] distance.
Mars as usual.
In the quartile near Zeta Tauri the lowest of two is a curious either nebulous star or perhaps a Comet.
A small star follows the Comet at 2/3rds of the field’s distance.111
There are no further remarks for these nights, and certainly no expression of excitement or anticipation. On the following night, Wednesday, 14 March, it was either cloudy, or Herschel did not bother to observe, for there is no entry. He may have been prevented by an official engagement to play the harpsichord at the Bath Theatre, or to rehearse oratorios with Caroline.112 On 15 March there are short observations on Mars and Saturn, accompanied by some drawings of them made between 5 and 6 a.m., but nothing further about the ‘curious nebulous star or comet’. On Friday, 16 March there is again no entry. But Herschel may have been reflecting on his sightings, and talking to Caroline over the weekend, for finally, on the night of Saturday, 17 March there is the first clear sign that he was definitely in pursuit of the mysterious new object.
Saturday March 17
11pm. I looked for the Comet or Nebulous Star and found that it is a Comet, for it has changed its place. I took a superficial measure 1 rev, 6 parts and found also that the small star ran along the other [cross] wire … Position exactly measured 91’96 …
Once Caroline had returned to New King Street on the twenty-first, there are regular entries in late March following the ‘comet’, and attempts to measure its diameter with William’s newly designed micrometer. For example, on 28 March the Observation Book reads: ‘7.25 pm. The diameter of the Comet is certainly increased, therefore it is approaching.’113 The increase in apparent size was a further indication of ‘proper motion’ and a solar orbit; and further proof that it could not possibly be a fixed star. But if it was a comet, there should be a slightly blurred, fiery outline and a distinct tail or ‘coma’. Here Herschel’s beautifully clear reflector images, even more than his high-magnification eyepieces, came into their own. In early April, some three weeks after his first sighting, Herschel made what seemed to be a definitive observation.
Friday April 6
I viewed the Comet with 460 [magnifications] pretty well defined, no appearance of any beard or tail. With 278 [magnifications] perfectly sharp and well defined.114
Though Herschel was scrupulously careful not to say so in his Observation Book, the sharp, round definition and the lack of any tail could only mean one thing: a new ‘wanderer’, or planet. What in fact he had observed was the seventh planet in the solar system, beyond Jupiter and Saturn, and the first new planet to be discovered for over a thousand years (since Ptolemy). He would name it patriotically after the Hanoverian king, ‘Georgium Sidus’ (‘George’s Star’), but it eventually became known to European astronomers as Uranus. ‘Urania’ was the goddess of astronomy, and the new planet was seen to mark a rebirth in her science.♣
Yet there was no Eureka moment: quite the opposite. For the next few weeks there was a great deal of uncertainty about what sort of astronomical body Herschel had found. Nowhere does the word ‘planet’ appear in his Observation Journal for that spring of 1781, and there was no popular reporting of the news in the magazines. The following year, when the sensation was widely known, it would be very different, as Caroline remarked: ‘Since the discovery of the Georgium Sidus, I believe few men of learning or consequence left Bath before they had seen and conversed with its discoverer.’ But for the time being there were just endless measurements with the micrometer, ‘and a fire to be kept in, and a dish of Coffee during the long nights of watching’. She added wryly: ‘I undertook with pleasure what others might have thought a hardship.’115
On 22 March Herschel tentatively communicated his preliminary observations of ‘a Comet’ to William Watson, who passed them on to Nevil Maskelyne and Joseph Banks at the Royal Society116 Maskelyne immediately contacted other European astronomers, notably Charles Messier in Paris, asking for their opinion.117 A week later Herschel followed this up with a direct report to the Royal Society, which was logged in the Society’s ‘Copy Journal Book’ for 2 April. Now he expressed barely muted excitement: ‘Saw the Diameter of the Comet extremely well defined and distinct; with several different powers thro’ my 20 foot Newtonian reflector. It was a glorious sight, as the Comet was placed among a great number of small fixt stars that seemed to attend it.’118
Remembering Herschel’s ‘lunacies’ of the previous year, Maskelyne was initially sceptical. He found great difficulty in even locating the new object with his own telescopes at Greenwich, a difficulty increased by Herschel’s inability to provide the conventional mathematical coordinates. At this stage Herschel located all his stars on hand-drawn star maps — what he called ‘an eye-draught’ — an amateur technique that again visually recalls his familiarity with musical scores.119 It was not until 4 April that Maskelyne wrote cautiously to Watson (still not to Herschel directly) that he had finally found the new ‘star’, and observed that it had just discernible ‘motion’. However, he prudently, and not unreasonably, hedged his bets: ‘This [the motion] convinces me it is a comet or a planet, but very different from any comet I ever read any description of or saw. This seems a Comet of a new species, very like a fixt star; but perhaps there may be more of them.’ This safely covered all the options. He added a pointed postscript: ‘PS I think [Herschel] should give an account of his telescope, and micrometers.’120
The Astronomer Royal was in a dilemma. He had no reason to accept Herschel as a reliable astronomer, and to declare a new planet prematurely might bring himself and the Royal Society into disrepute, and even ridicule. On the other hand, to reject what might be the greatest British astronomical find of the century, especially if the predatory French astronomers accepted it first (and even named it), would be even more damaging. He was also aware that Banks regarded this as a crucial moment in his presidency, and in the fostering of good relations between the Royal Society and the Crown. King George III was particularly fascinated by stars, and particularly keen to outdo the French.
Maskelyne finally chose to act as a man of science: he went back to his own telescopes, and from 6 to 22 April made his own observations. He was, after all, acting precisely according to the motto of the Royal Society itself: Nullius in Verba – ‘Nothing upon Another’s Word’. On 23 April he at last wrote directly to ‘Mr William Herschel, Musician, near the Circus, Bath’. He began prudently, but ended firmly.
Greenwich Royal Observatory, April 23, 1781
Sir, I am to acknowledge my obligation to you for the communication of your discovery of the present Comet, or planet.
I don’t know which to call it. It is as likely to be a regular planet moving in an orbit nearly circular round the sun, as a Comet moving in a very eccentric ellipsis. I have not yet seen any coma or tail to it …
This tipped the argument towards a
planet, but was not a decisive opinion. Maskelyne then went into technical details about their respective telescopes — especially the need for ‘very firm stands’ — and the difficulties of using micrometers to measure apparent changing diameters (and hence establish a possible planetary orbit): ‘If the light of the small planet is not still, & free from scintillations, it is impossible to prove it to have any other than a spurious diameter that may arise from the faults to which the best telescopes are subject.’ Nonetheless, he praised Herschel for making ‘very good observations’.
Finally, in his last paragraph, he committed himself. ‘On the 6th April I viewed the Comet with my 6 foot reflecting telescope and the greatest power 270, and saw it a very sensible size but not well defined. This however showed it to be a planet and not a fixt star, or of the same kind of fixt stars as to possessing native light with an insensible diameter. I am Sir, etc etc, N. Maskelyne.’121
Herschel had gained an invaluable ally. He immediately sent up a brief, masterly paper which was read at the Royal Society on 26 April. It was entitled simply ‘An Account of a Comet’, and was published in the Philosophical Transactions in June. He stated that ‘between ten and eleven in the evening’ of 13 March 1781 he had at once recognised a new object of ‘uncommon magnitude’ in Gemini, and immediately ‘suspected it to be a comet’. But from the account he then gave of its magnitude, clarity of outline and ‘proper motion’ it was clear that Herschel was now claiming that the ‘comet’ was really a new planet. Though, no doubt advised by Watson, he did not actually say so. To support this, he also claimed that the object remained perfectly round, without the least appearance of comet’s tail, when magnified 270, 460 and 932 times — the latter magnifications being far beyond what even Maskelyne’s Greenwich telescopes could achieve. All this naturally excited even more controversy than his moon paper, and some murmurs of dissent.122
The Age of Wonder Page 14