Herschel made exquisitely detailed drawings of botanical specimens, which Margaret colored; these lovely paintings are cosigned by the two of them.34 Together they produced 131 botanical illustrations of high scientific and artistic quality. To make these drawings, Herschel employed considerable skill with the camera lucida. This device had been patented by W. H. Wollaston in 1807, after he developed it for the purpose of recording his observations during a geological tour of the Lake District; but similar instruments existed earlier (the American artist David Hockney has controversially argued that many Old Master painters, such as Caravaggio, Velázquez, and Leonardo da Vinci, used the camera lucida to sketch their canvases before applying the paint).35 Wollaston had found that by perching a prism with one reflective surface on an adjustable brass stem, and mounting this on a drawing board, one could peer down on the prism in such a way that the scene before him would appear to be projected on the paper below. This was just an optical illusion—the image was not really on the paper—but by tracing the image that appeared to be there, the artist could capture the scene in incredible detail.36
Once Wollaston’s device became widely available, many scientists felt that a huge burden had been lifted off their shoulders. This instrument allowed even those with less than impressive artistic skills to capture the scientific observations they were making; at this time, before photography, scientists working in the field or in the laboratory had to draw what they saw in order to transmit their observational results to others. The scientist had to be also an artist, a situation to which Whewell may have been gesturing when he coined the word scientist “by analogy with artist.” One convert to the device rhapsodized that “with his sketch book in one pocket, the Camera Lucida in the other … the amateur [artist] may rove where he pleases, possessed of a magical secret for recording the features of Nature with ease and fidelity, however complex they may be, while he is happily exempted from the triple misery of Perspective, Proportion, and Form,—all responsibility for these taken off his hands.”37
John and Margaret had used the camera lucida extensively on their honeymoon (when they were not visiting factories). Herschel liked the device because it allowed the man of science to observe and capture on paper nature more closely—indeed, more truthfully—than was possible without it. A sketch from nature itself could only depict what the eye happened to see casually; a drawing done with the camera lucida captured more detail than the observer was likely to notice on his own. Herschel saw this device as allowing the kind of complete accuracy that he, Babbage, and Whewell had been advocating since the days of the Analytical Society. Later he would realize that an even more accurate depiction of nature was possible with the photographic technology he would help develop.
Margaret gleefully reported to Aunt Caroline how happy they were at the Cape, especially her husband: “Nothing can be better than his health during the whole winter,” she wrote at the end of September 1834, “indeed he looks ten years younger, and I doubt if he ever enjoyed existence so much as now for there are not the numerous distractions which tore him to pieces in England, and here he has time to saunter about with his gun on his shoulder and basket and trowel in his hand—I sometimes think we are all too happy, and life goes too smoothly with us.”38
HERSCHEL’S NIGHTLY SWEEPS were bearing fruit. Over the course of his four years at the Cape, Herschel made a number of discoveries, and charted a large portion of the southern hemisphere, creating a map that would provide guidance for ship captains gliding over the waters of that part of the world for more than a hundred years.
By the end of his stay, Herschel had conducted the most thorough astronomical survey ever done of the region, an accomplishment that would not be improved upon until the mid-twentieth century. He compiled a catalog of 1,707 southern nebulae, only 439 of which were known previously, as well as a catalog of 2,102 double star pairs. Continuing his father’s work of providing “star gauges,” which showed the density of stars in different parts of the sky, he counted the total number of stars—nearly 70,000—in 3,000 slices of the heavenly vault, providing statistical data about the distribution of stars in the Milky Way system. (He spent several months mapping a minute speck of space—which would have been eclipsed by the tip of his wife’s pinky finger held at arm’s distance from the eye—containing 1,216 stars.) This mapping led Herschel to the conclusion that the structure of the galaxy was ring-shaped, rather than a flat disk, as his father had thought, with many stars crammed together at the edges and blank spaces with no visible stars in the middle (it was not discovered until much later that these apparently starless zones in the Milky Way are not real holes, but an effect of opaque clouds of dust and gas).39
As part of his work, Herschel invented an instrument to determine the relative apparent brightness of stars—how bright they seem to us compared to the sun. Before Herschel, astronomers had been forced to make visual estimates of relative brightness. But such estimates varied from observer to observer, and so remained highly subjective. A method to determine the apparent brightness of a star with greater precision would be useful because then astronomers could classify stars by their apparent brightness into groups, and also because, knowing the apparent brightness and the distance of the star, the astronomer could determine the absolute brightness, how luminous the star really is. For instance, we know now that the sun is really just a star of average luminosity—we see it as exceedingly bright because it is so close to us.
Herschel’s “astrometer” was the first stellar photometer. It allowed the user to determine the apparent brightness of a star using a scale based on the reduced image of the moon. He made the astrometer by mounting a reflecting prism on a wooden platform (similar in some respects to the camera lucida) in front of the telescope eyepiece. By rotating the prism, the light of the moon could be directed to the eye in such a way as to appear to come from the same direction as the light from a given star. A lens mounted between the eye and the prism reduced the size of the image of the moon until it was a mere point, an “artificial star.” The brightness of this artificial star could be varied by moving the lens closer to or farther from the eye, until the real and artificial stars appeared equally bright. The distance between the eye and the lens would give a measure of the apparent brightness of the real star.40 Herschel eventually used his astrometer to measure the brightness of 191 stars in both hemispheres.
What Herschel saw with his telescopes often amazed and delighted him. In early 1835 it was time for the periodic return of Halley’s Comet. Herschel observed the comet closely for several months, describing it to Francis Beaufort as “altogether the most beautiful thing I ever saw in a telescope.”41 He viewed the seven known satellites of Saturn, two of which had been discovered by William Herschel and not seen since. John triumphantly wrote to Aunt Caroline, “I have at last had the pleasure of seeing what only my father had ever seen before Saturn surrounded by all his seven companions at one view Really a fine family!!”42 He carefully observed the Magellanic Clouds, two enormous star clusters near the Milky Way belt, visible only in the night sky of the southern hemisphere. Herschel painstakingly sketched what is still considered the best hand-drawn map of the Large Magellanic Cloud prepared by an observer directly from his or her telescopic results; showing 1,163 stars, it has been called “a masterpiece of celestial topography.”43 And he examined the wonderful grouping of stars in the constellation of Crux, the Kappa Crucis cluster. The cluster is known as the “Jewel Box” because Herschel referred to its extravagant mix of red and blue stars as having “the appearance of a rich piece of jewelry.”44
Herschel carefully observed sunspots—those dark spots that appear at times on the surface of the sun—making drawings that carefully traced the tracks of the spots in their rotation around the sun. His father had been among the first to notice the periodic nature of the spots: he had realized that they appeared with greater frequency in certain years. Using Smith’s Wealth of Nations as his source, William Herschel correlat
ed the times of high sunspot activity with periods of lower wheat prices, suggesting that large numbers of sunspots indicated a warmer sun, which increased crop yields on earth, depressing grain prices. Although the elder Herschel was ridiculed for his theory that sunspot activity correlated with weather patterns on earth, scientists now believe that he was correct.45 At the end of the nineteenth century, the economist Stanley Jevons would put forward the idea that the sunspot cycle might influence the business cycle, by having an impact on the climate.46
Careful not to make any excessive claims as his father did, John Herschel called for a permanent watch on sunspot activity, and simultaneous recording of meteorological data, carried out by observatories around the world.47 And when he finally published his huge work detailing all of his observations during his Cape Expedition, in 1847, Herschel would point to the new technology he and his friend Talbot pioneered, suggesting that astronomers begin to keep a photographic record of the changing appearance of sunspots.48
IN EARLY 1837, Herschel began to wrap up his work at the Cape. He wrote to Aunt Caroline that he was commencing the “reduction and arrangement of the mass of observations accumulated.”49 The raw data from the many thousands of observations made by Herschel needed to be put into a form in which it could be analyzed to determine the precise positions and distances of stars and other celestial objects. It was wearying work; after four years of good and hearty health, Herschel was suddenly plagued with rheumatism attacks and migraine headaches.50 Although the years of observing in the cold winter night, and all the mathematical reduction of data he was engaged in, might have caused these symptoms, it is difficult to avoid the conclusion that the very thought of returning to England was sickening Herschel. He made it clear that he wanted to avoid getting caught up in all the public work of science from which he had escaped four years earlier. Herschel told his brother-in-law that the family would leave for Hanover soon after returning to England, as a way to avoid the August meeting of the British Association. “Not that I mean to abuse that Institution,” he equivocated, “but … really there has crept into their meetings a style of mutual be-buttering the reverse of good taste.… I don’t want to be drawn into any of their work for the next year at least, having quite as much on my hands as I can possibly accomplish without taking any extra duty.”51
Herschel began to dismantle the telescopes in February 1838. The family packed up their possessions, said farewell to their happy home, and embarked on the ship Windsor on Sunday, March 11. The passage homeward was beset with worse weather than they had faced coming out; nevertheless, Herschel resumed his meteorological readings and his dissections of sea life. They arrived home on May 15, 1838. Herschel would, for the rest of his life, think back to that time at the Cape as “the sunny spot in my whole life where my imagination will always love to look.”52
Upon his return to England, Herschel was thrown a huge banquet, held at the Freemasons’ Tavern, to celebrate his safe return and his being declared a baronet by the new young queen, Victoria. (Herschel had previously been knighted, and so was already known as “Sir John,” but the baronetcy was a title that would pass down to Herschel’s oldest son, and on to future generations.) Babbage, Jones, and Whewell were all there to welcome him home.
THE VERY DAY that Herschel and his family set sail for Africa in November of 1833, Whewell, now thirty-nine, turned his thoughts to the seas, telling Jones that he was working on “a thumping paper on the Tides.”53 By the time Herschel returned from the Cape, Whewell had organized the first international investigation into the tides, and had used the resulting data to draw a comprehensive and remarkably accurate map depicting the movement of the tides throughout a large part of the world’s oceans.
The ebb and flow of the sea was bound to be important to Britain, which had emerged after the Napoleonic Wars as the world’s most important maritime nation. It is, after all, an island surrounded by water: no one on it lives more than seventy miles from a coast. By the 1830s, Britain had the world’s most advanced system of river, canal, and coastal transportation. Its trade depended on reliable routes for shipping necessities like coal from port to port, as in the case of the Lancaster canal in Whewell’s youth, transporting coal from Preston to Tewitfield and limestone from Tewitfield to Preston. Most of those ports were estuary ports, where access depended entirely on the rise and fall of the sea; at some ports, such as Newcastle, ships could only reach the docks during extreme high water, which lasted less than an hour.54 In order to safely dock their increasingly larger and iron-hulled ships at port, captains needed to know when the tide would be high, so that the ships would not run aground on the shallow sea bottom.
But more than just trade was at stake: exploration and naval defenses were also tied to the tides. An article in the Transactions of the Royal Society in 1819 argued provocatively that because Lord Nelson had miscalculated the tides at the straits of Dover, the ships he sent to attack the French flotilla in Boulogne Bay in 1801 did not arrive until it was too late.55
Shipwrecks were common. Although Herschel and Babbage had used the specter of ships lost on the high seas to argue for funding to build the Difference Engine, it was actually more common in the early nineteenth century for ships to sink close to ports. Strange as it sounds, most seamen did not know how to swim, so even within sight of land, all hands could be drowned.56 More than a thousand British ships, and their crews, were lost each year.57
The tides of the Thames River, winding through England, had long been seen as dangerous as well. The waters of the Thames would sometimes simply appear beside the old docks, which were without steps or wharves, so suddenly that the unwary pedestrian might be sucked into the river’s depths. Suicides were drawn to the dark, flowing water, and their bodies often washed up along the river’s shore during low tides. The river was a convenient place to hide corpses of murder victims, which sometimes also ended up on the shores of the river when they were not discreetly carried to the sea.58 The Thames had become even more dangerous in recent times. Increased shipping had led to the building of more docks, especially in London. But the construction of those docks—as well as bridges, embankments, and other large-scale projects on the Thames—obstructed the flow of the river, which reacted violently. Tides rose over the newly constrained banks, flooding low-lying neighborhoods. In one notable incident, the tides flowed over the Blackfriars Bridge in December 1814, flooding Windsor Park and inundating warehouses and businesses nearby.59
Yet, oddly, given the extreme importance of water to Britain, knowledge of the tides was still extremely scanty. Two centuries before, Francis Bacon had suggested an international system of tidal observations to remedy the situation, yet his call had gone unheeded. The only people who systematically observed the times of the high and low tides were harbormasters, and they tended to keep their information as closely guarded secrets: few accurate tide tables based on long-term observations were published and made readily available. The Royal Navy had no such information; captains were responsible for trying to gain the information on their own, by contacting harbormasters and hoping to get useful information from them—usually by paying them bribes to share their knowledge.
Not only was empirical information about the tides incomplete and inaccessible, but detailed theories of the tides were also lacking. Newton had believed that the tides were caused by the mutual gravitational attraction of the moon, sun, and the water on the earth, which was basically correct. (Even before Newton, medieval clocks and tide tables had assumed that the tides were related to the phases of the moon, but this was not expressed in terms of any particular law.)60 Newton established that the attractive forces of the sun and moon produced a tide-generating force; but it still remained to be shown how the law of universal gravitation could account for particular tides.61 His theory as applied to the tides did correctly predict some of the observed phenomena, such as the known fact that the oceanic high tides lag roughly three hours behind the syzygies (when the sun, earth, and mo
on are aligned, which happens at the time of the full moon and the new moon). But Newton’s analysis was inconsistent with many of the observations that did exist, indicating that the relation between the tides and the gravitation between the earth, sun, and moon was still not fully understood.62 In particular, his theory did not provide any understanding of factors that might counteract the attractive force.
Later, Pierre-Simon, Marquis de Laplace, mathematically defined the dynamic relations that determine the ocean’s responses to tidal forces. His tidal equations were extremely difficult to solve—indeed, real solutions became possible only with the use of large digital computers in the last decades of the twentieth century.63 Laplace himself could calculate solutions only for the idealized situation of an ocean of uniform depth completely covering the globe. He could not, that is, take into account the effect of the continents and the shapes of their shorelines, the presence of rivers and canals and other narrow bodies of water, differing oceanic depths, and other factors. Laplace’s “oscillation theory,” as it was called, was nevertheless able to account for certain observed effects. Yet, like Ricardo’s axioms in political economy, its simplifying assumptions only served to render false or irrelevant any conclusions drawn from them. As Whewell would later explain to Lyell, Laplace’s speculations could not even count as approximations, because the hypothesis of a “universal ocean” rendered them useless.64
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