The Philosophical Breakfast Club (42 page)

Once he relocated, Herschel devoted himself to making all the necessary calculations from the data gleaned from his four hundred nights of observations at the Cape Colony. It was a long and irksome process, one that he conducted himself, without the help of paid computers. His friends, especially Whewell, lamented the lavish expenditure of his time and effort upon “mere arithmetic.” Whewell tried to persuade him to hire assistants, but Herschel persisted in his solo labors. It would take over seven years before Herschel completed the work. During this time he was constantly pulled between his need to finish the calculations and his desire to experiment on photography. Margaret admitted to Caroline during this time that she had not given up “
spurring
him on with his Cape calculations, for so much of his valuable time was spent in making these observations, that I am determined
not to be happy
until the work is completed and out of his hands. Am I not a very cruel wife!” John lamented to her, “Don’t be enraged against my poor photography. You cannot grasp by what links
this
department of science holds me captive—I see it sliding out of my hands while I have been
dallying
with the stars.
Light
was my first love! In an evil hour I quitted her for those brute and heavy bodies which tumbling along thro’ ether, startle her from her deep recesses and drive her trembling and sensitive into our view.”
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After a winter in which there were fogs so thick and opaque that ships routinely collided,
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the sun finally broke out, and Herschel could not resist returning to his experiments in the spring of 1840. As Talbot wrote to him, “The present weather is the fairest and most settled, since the birth of photography.” Herschel soon told his aunt that “we have had and are still having a most magnificent summer—such a one as I do not remember ever before in England.”
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At the end of August, Herschel succeeded in producing a color photograph of the entire light spectrum. By concentrating the prismatic spectrum with a large lens of crown glass, and aiming it onto the prepared paper, Herschel found that the resulting image was tinged with colors that differed based on their location on the spectrum: red rays gave no tint, orange a faint brick red, the orange/yellow rays a pretty strong brick red, the yellow a red passing into green, the green a dull bottle green passing into blue, the blue/green a dull and somber blue, almost black, the blue a black, the violet a black passing into yellow with long exposure, the part beyond the violet (the ultraviolet), a purplish black.
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Herschel excitedly told Talbot that “it holds out I think a very fair promise of solving the problem of coloured Photographs!”
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By the fall of 1840, Talbot too had made a breakthrough, one that secured his method’s success over Daguerre’s. He found a way to amplify the effect exerted by light in his camera. He discovered that a weak exposure, because of darkness or haze, insufficient to produce a visible image, could be brought out by an additional wash of gallic acid and silver nitrate. That is, the latent image could be made apparent. Talbot immediately began to speculate on the types of objects that could be photographed: “Sun behind a cloud. Moon. View by moonlight. Fire. Lighted candle. Vase, at first screened from sunshine.… White clouds. Diffraction bands. Spectrum.”
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No longer did Talbot’s method rely wholly on the sun to reduce the silver on the photographic paper. Now he could take a faintly exposed photographic plate and amplify the exposure through chemical means. He called the new type of images “calotypes,” for the Greek
kalos
, or “beautiful.” In December of 1840, Herschel was distressed to learn that he, and not Talbot, had been awarded the gold medal of the Royal Society for work on photography, specifically for his paper on the photographic action of the solar spectrum. In 1842 the Royal Society finally recognized Talbot’s achievement, and awarded him its prestigious Rutherford medal for his work.

H
ERSCHEL’S INTEREST
in botany, born during his time at the Cape Colony, was put to use in his photographic experiments. Herschel began to experiment with floral dyes, using the petals of fresh flowers in the place of the silver salts to produce photographic papers. He would crush the flower petals to a pulp in a marble mortar, sometimes with the addition of alcohol. The juice expressed by squeezing the pulp into a clean linen or cotton cloth was spread on paper with a flat brush, and dried in the air.
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The benefit of this process was that while the silver salts darkened when exposed to light, the dyes usually bleached under the exposure, thus producing a direct positive. Herschel’s experiments showed that different extracts produced different tints under varied wavelengths of light. This process yielded rich single-color photographs, many of which remain vivid today. Had Herschel persisted in these experiments, he would almost certainly have produced a full-color photograph, by superimposing different-colored layers with sensitivities to different primary colors.
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He submitted fifteen colored photographic copies of engravings and mezzotints—prepared by casting luminous rays on substances derived
from plant sources—to the Physical Section of the British Association meeting in 1841.
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One of his color processes used an iron pigment known as Prussian blue rather than vegetable dyes. This process, dubbed by Herschel the “cyanotype,” became the most commercially viable of the paper photographic methods in the 1840s, and survived into the twentieth century as the basis of the architect’s blueprint. By washing paper with a solution of ferric ammonium citrate, an iron salt, Herschel created photographic paper highly sensitive to the action of light. After half an hour or an hour’s exposure to sunshine, followed by a wash in a solution of yellow potassium ferrocyanate, a white image would appear on a bright blue background.
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This cyanotype process led to the publication of the first book to use photography: Anna Atkins’s
Photographs of British Algae: Cyanotype Impressions
, first part published in 1843. (Talbot would not publish the first volume of his own book,
The Pencil of Nature
, until the following year.) Anna Atkins was the only daughter of John George Children, who had been a friend of the Herschel family since youth—he was also a sworn enemy of Babbage, having won out over Babbage for the job of junior secretary of the Royal Society in 1826. Anna had been raised by her father after her mother’s death in childbirth, receiving from him a highly scientific education, which was still quite unusual for a woman of her time. She also had access to his large and well-equipped laboratory, which had been the setting, in 1813, for the convergence of thirty-eight of Britain’s leading chemists—Wollaston and Davy among them—for dinner and a demonstration of Children’s huge voltaic battery.

As a young woman, Anna produced 250 detailed engravings to illustrate her father’s translation of Jean-Baptiste Lamarck’s classic work,
Genera of Shells
. In 1825 she married John Pelly Atkins and moved to Halstead Place in Kent, where she began a collection of dried plant specimens later donated to the Botanical Gardens at Kew. She was made a member of the Botanical Society of London in 1839—it was one of the first scientific organizations to admit women as full members (her father was, at the time, the society’s vice president).

Children and his daughter knew Talbot and Herschel well. Atkins probably knew Richard Jones as well; his home in Sevenoaks was only five miles from Halstead Place, and Herschel was a frequent visitor to both Atkins and Jones. Children had been the chair of the Royal Society meeting
when Talbot discussed the details of his process of photogenic drawing in February 1839, and he would have discussed it with his daughter soon afterwards. In 1841 Children told Talbot that he had ordered a camera for Anna.

During the summer of 1843 Atkins began working on a book about algae, using the cyanotype method of photography. In her preface she explained that “the difficulty of making accurate drawings of objects as minute as many of the Algae and Confervae, has induced me to avail myself of Sir John Herschel’s beautiful process of Cyanotype.”
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It is likely that Herschel himself had taught her the process. By October she began issuing parts of the book. Each part consisted of a series of original cyanotype plates that were contact prints, made by placing specimens of algae that had been washed, arranged, and dried on top of a sheet of prepared paper, and set in the sun; the exposed sheet was then washed, dried, and flattened. The resulting book consisted of 389 captioned plates, and fourteen pages of titles and text. At least a dozen copies of the book were made and distributed to interested scientists, including Talbot and Herschel (Herschel’s copy now resides in the collections of the New York Public Library). This means that Anna, perhaps with the help of her father, prepared thousands of sheets of cyanotype paper by hand. His giant battery could have been used to produce the ferric ammonium citrate and the potassium ferrocyanide needed for the process. This monumental accomplishment took ten years to complete. Not only was the cyanotype method relatively inexpensive and long-lasting, but it produced a deep blue color that was particularly appropriate for the algae, which appear to be floating ethereally in a cerulean sea.
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A
LMOST AS SOON
as the new technology had been invented, Herschel began to devise plans for harnessing it to the train of science. He encouraged Anna Atkins in her work, pleased to see photography put to the use of botany, an improvement over the botanist’s former reliance on the camera lucida. Herschel also saw that photography would be valuable in astronomical observations, particularly for the recording of sunspot activity. First, though, a means needed to be developed for the sun’s light to be used for making an image without overexposing it. Warren de la Rue would soon invent a device that could take solar photographs, and it would be deployed at the Kew Observatory for making the observations
suggested by Herschel. But before then, Herschel had a chance to attempt to introduce photography into an expedition being readied for the Antarctic region, an expedition he and Whewell were responsible for promoting.

While at the Cape of Good Hope, Herschel had been making hourly observations of weather phenomena on the days of the equinox and the solstice: the equinox occurs twice a year, in March and September, when the sun is vertically above a point on the equator; the solstice, when the sun’s position above the earth is at its northernmost and southernmost extremes, also happens twice a year, in June and December. One typical diary entry reads: “Rose at 5½ and commenced hourly observations for the Month—which I carried on till 4 AM of the 22
^nd
when Marg
^t
relieved me and took the 2 last hours.”
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Another: “At 6 AM began the Hourly Obs
^ns
for the Winter Solstice.…—Occupied with them the whole day.—at 5PM went to bed. Got up at 9 and sate up all through the night and till 3 sweeping the intervals.”
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Barometric pressure, air temperature, and the intensity of light from the sun were all measured. At the same time Herschel was soliciting meteorological observations from colleagues around the globe: Albany and Boston in the United States; Mauritius; Brussels; Van Diemen’s Land (now Tasmania); and others.
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Part of his motivation was to gather the data that might make it possible to confirm his father’s suspicions about the correlation between the weather and sunspots. Did periods of greater sunspot activity mean more sunlight reaching the earth’s atmosphere, or more cloud cover: more light or more shadow? (Solar scientists are still debating this question today.) But another issue at stake was the relation between atmospheric conditions and the intensity of terrestrial magnetism.

As William Gilbert had concluded in 1600, in his monumental work
De Magnete, magneticisque corporibus, et de magno magnete tellure (On the Magnet, Magnetic Bodies, and the Great Magnet the Earth)
, the earth is a giant magnet, with north and south magnetic poles. This was why, Gilbert argued, compasses always pointed north, a fact that had been known for centuries, but had previously remained unexplained.

The use of the nautical magnetic compass had made possible the “age of exploration” and the increased trade, naval defenses, and imperialism that went with it. For this reason, Gilbert’s contemporary Francis Bacon considered the compass one of the three technologies that defined the modern age (the others were the printing press and gunpowder). But
no one had yet been able to account for just how the magnetic compass enabled sailors to find their way around the seas.

By describing his experiments showing that the earth was a giant magnet, Gilbert provided such an explanation. The compass did not point north because of a magnetic Pole Star, as Christopher Columbus had thought, or because of a large magnetic island at the north geographic pole, as others had previously speculated. Rather, it pointed north because it was being attracted to a magnetic pole of the earth. Gilbert correctly reasoned that the core of the earth was iron, thus explaining the earth’s magnetic force.

Like Bacon, Gilbert emphasized the importance of drawing conclusions from experiments and observations, and rejected the scholastic Aristotelianism. (This did not stop Bacon from accusing Gilbert of having “made a philosophy out of a few experiments,” mostly because he posited the existence of a kind of “magnetic soul” in the earth.)
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Gilbert created a model of the earth—which he called a
terrella
, for “little earth”—by forming a sphere out of a lodestone, a naturally magnetized mineral. He then devised a
versorium
, or “turn-detector”—a miniature needle, mounted so it could rotate freely in three dimensions. Moving the versorium over the surface of the terrella, as if it were a ship sailing over the surface of the earth, Gilbert identified the location of the magnetic poles by observing where the needle stood vertically. He also found that the “dip” in the needle increased steadily from zero degrees at the equator to 90 degrees at the poles, which he realized could be an accurate way to determine latitude while at sea.
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