The Philosophical Breakfast Club (29 page)

When the passengers disembarked, feeling a bit unsteady on solid ground after so long at sea, they were overwhelmed by the sight and sounds of a military parade. “The streets were lined with the military,” the
Cape of Good Hope Literary Gazette
reported, “colors were everywhere flying,
and the Artillery fired a salute.… [T]he whole population of Cape Town had turned out in the streets or were at the windows or tops of Houses.” They were celebrating the arrival of the new governor of Cape Town, Sir Benjamin D’Urban, who had traveled on the
Mountstuart Elphinstone
with the Herschels.
¹⁷
To the Herschels, the pomp and ceremony seemed to presage a successful stay.

The family found themselves in what John Herschel would call “a sort of earthly Paradise,” filled with 250 species of birds, numerous kinds of antelope, lizards, snakes, tortoises, insects, mongoose, baboons, otter, deer, and zebra, and over 1,100 species of indigenous plants (maybe too much like Paradise, Herschel mused, when he had to chase a poisonous snake out of the children’s nursery).
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Cape Town, thirty-nine miles to the north of the Cape of Good Hope, was originally a resupply camp for the ships of the Dutch East India Company. Among sailors it was known as the “Tavern of the Seas,” because they would stop there to take on fresh provisions during the long journey around Africa. The British, who had occupied the area around the Cape intermittently, were granted the colony in the Anglo-Dutch Treaty of 1814, and it would remain a British colony until it was incorporated into the independent Union of South Africa in 1910. In 1820 the British government had established an observatory there, but it was not yet very well equipped. Herschel’s private observatory would best the royal one both in equipment and personnel.

John and Margaret rented a spacious Dutch farmhouse about six miles southeast of Cape Town, situated at the foot of Table Mountain, a sandstone monolith soaring 3,550 feet above sea level, topped by the tablelike summit that gives the mountain its name. The house, called Feldhausen, was surrounded by large orchards and a grove of oak and fir trees as well as a profusion of native flowering plants. Herschel confided to his diary that it is “really one of the most magnificent sites for a home I ever saw; with every combination of wood, mountain and water which can give a charm to the landscape scenery.”
¹⁹

As soon as the baggage had been transported to the house, Herschel and Stone began setting up the new observatory. Herschel had brought the twenty-foot reflecting telescope, and three interchangeable mirrors for it: one made by his father, one made by father and son together, and one by the son on his own soon before departing. At this time mirrors were made not of metal-coated glass, as they are today, but of “speculum metal,” a white metal alloy of copper and tin with a pinch of arsenic. This
metal was very prone to tarnish, and needed frequent repolishing, an operation that altered the shape of the mirror slightly, so that it needed to be refigured each time. When one mirror became imperfect, Herschel would be able to replace it with one of the others, while he worked laboriously on repolishing and refiguring the tarnished one.
²⁰
This happened frequently, about every six days—the mirror was besieged not only by the salty sea air, but also by extreme temperature changes; the weather varied from cold and windy nights during which the astronomer’s fingers would become stiff with cold, to days so hot that Herschel could cook a mutton chop and potatoes in the sun and eat them.
²¹
Stone oversaw the construction of a giant framework mounted on movable rollers, from which the telescope was suspended by ropes. A movable platform gave the observer access to the eyepiece from a variety of positions.
²²

Herschel had also conveyed to the Cape the seven-foot equatorial refractor he and South had used for their double-star measurements. Attached to this telescope were the graduated circles and micrometers useful for the precise measurement of the distances between double stars. As these instruments needed to be shielded from the elements, the seven-foot refractor was not left out in the open with the other telescope, but was housed in a newly built private observatory with a sliding roof that opened and closed as needed. The twenty-foot reflector was already in use by February 22, but the smaller refracting telescope was not ready until May.
²³

When Herschel first gazed into the eyepiece of the twenty-foot reflector, he was shocked to discover that, as he complained to his aunt Caroline, “in spite of the clearness of the sky the stars are ill-defined and tremulous.”
²⁴
It seemed that the atmosphere was not conducive to making the planned observations. For a time Herschel secretly feared that his whole expedition was doomed. But he was soon pleased to report that he had had “a
perfect
Astronomical Night.—I hereby retract all I have said in disparagement of the Cape Atmosphere.—Such tranquility and definition of stars equals anything I have ever had in England.”
²⁵
He later described another night’s sweep as “
the Sublime of Astronomy
—… an epoch in my Astronomical life.”
²⁶
He would find that the observing conditions were best during the winter season, from May to October, especially right after the heavy rainstorms common during that period.
²⁷

Once they were settled in, Margaret and John began a routine that would last for the entire duration of their time at the Cape Colony. John
spent his nights sweeping the sky, with the assistance of Stone. They did the sweeps just as they had in England: the twenty-foot telescope would remain pointed at the same direction in the sky, being moved (by Stone) up and down slightly, only enough to “sweep” three degrees of width in the sky (remember, the celestial sphere is divided into 360 degrees, like a solid sphere). Small bells were attached so that they would ring when the telescope reached the upper and lower limits of its sweep, alerting Stone to stop moving the telescope. Lateral motion came from the revolution of the heavens over the course of the night, which would bring new stars, clusters, and nebulae into view of the telescope. When they were finished for the night, usually around four o’clock in the morning, Herschel and Stone would retire to their beds. After sleeping late in the morning, Herschel passed much of the day with Margaret, riding, taking walks, visiting their neighbors, making detailed meteorological observations, measuring the sun’s radiation by exposing water to the sun and then measuring its temperature with a sensitive thermometer (a device he called an “actinometer”), and engaging in their new hobby, botanizing.

Herschel began to collect bulbs of the exotic and colorful flowers that grew indigenously at the Cape. One expedition to seek new bulbs with the whole family included his infant son Alexander, only six weeks old at the time. He kept diary entries on the growing and flowering of bulbs he planted on the Feldhausen property, recording whenever he decided to “make a gardening day of it.”
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He sent bulbs to his friends in England, including William Henry Fox Talbot.
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And he exchanged letters, samples, and descriptions of flowering plants with William Henry Harvey, a botanist who was also Colonial Treasurer of Cape Town. Harvey would later name a specimen of the orchid genus Satyrium after Lady Herschel.
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Another botanist, John Lindley, would name a group of ground orchids with blue flowers and narrow leaves Herschelias, referring to John Herschel not as the famous astronomer but as “the successful collector of Cape orchids.”
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Herschel proudly showed off his garden to all visitors, including Charles Darwin, who had eagerly anticipated his meeting with “the great Man” when the HMS
Beagle
docked at the port of the Cape in 1838, on the way back to England from the Galápagos Islands.
³²
(Darwin would enthuse in his diary after his visit that becoming acquainted with Herschel “was the most memorable event which, for a long period, I have had the good fortune to enjoy.”)
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When he returned to England, Herschel brought back with him crates of specimens, some of which he
planted in Slough, and others of which he donated to the Royal Horticultural Society.

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).
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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.”
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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.”
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H
ERSCHEL’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.