7. The Age of Wonder, by Richard Holmes, pp. 182-210

Herschel Among the Stars, 2-6

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In 1788, Herschel married Mary Pitt, a wealthy widow, causing something of a rift with Caroline, who found her role in the household suddenly shrunken. Caroline moved out of The Grove into an apartment above the stables, next to the observatory. She refused an offer of a quarterly salary of £10, but she still had the more generous stipend from the queen. Interestingly, she also destroyed her personal journals for the next decade, during which she moved out of the apartment and into the village of Slough. Whatever Caroline's feelings were about her brother's marriage, she continued to be his assistant and to do her own observations as well, discovering a second comet in December 1788. She also began a regular correspondence with the Royal Astronomer, Nevil Maskelyne.

The 40-foot telescope

In spring 1789, the great forty-foot telescope was finally completed. With it, Herschel discovered the tiny moon of Saturn called Mimas, which is only 250 miles in diameter and has a huge crater eighty feet across and six miles deep. (When the crater was photographed by Voyager in 1980, it was named Herschel.) The telescope became a major tourist attraction and was hailed as one of the wonders of the world. The visiting Oliver Wendell Holmes described it as looking like "a piece of ordinance such as the revolted Angels battered the wall of Heaven with." But it was something of a dud: hard to maneuver and far more subject to weather than the smaller telescopes. The mirrors weighed a ton, and had to be repolished annually. Removing them was not only difficult but dangerous -- Herschel was nearly killed in 1807 when a mirror slipped from its harness while being removed. In the five years from 1788 to 1793, Herschel recorded only seventeen nights of optimal observing conditions. It was also more useful for observations within the solar system than into deep space: Herschel added two more moons to the five that Saturn was already known to have.

Herschel began to do more revolutionary theoretical work. In 1789 he published a paper that expanded on his earlier "On the Construction of the Heavens," suggesting that the whole universe was in a state of change, being worked on by the force of gravity. He likened the skies to a garden in which we can "witness the germination, blooming, foliage, fecundity, fading, withering and corruption of a plant." The same process was at work in the stars.

In this paper, astronomy changed decisively from a mathematical science concerned primarily (for practical purposes) with navigation, to a cosmological science concerned with the evolution of the stars and the origins of the universe.

The Herschels were also experiencing personal changes: In 1792, Mary gave birth to their only child, a boy they named John. And Caroline had entered on a new phase of her career as an astronomer. She found her third and fourth comets in 1790, a fifth in 1791, and a sixth in 1793. She began a new Star Catalogue which would be published by the Royal Society and eventually replace the standard reference published by John Flamsteed in 1776. When she found a seventh comet in 1797, she was so excited she did something completely uncharacteristic: She rode a horse by herself from Slough to London, a distance of twenty-some miles, to tell Maskelyne the news personally. She also wrote to Joseph Banks, noting that the day was a historic one because she had never ridden more than two miles outside of Slough before. This excursion was followed by her move out of the apartment and into lodgings in Slough.

In 1791, William published a paper about nebulae in which he reported on a star that was surrounded by a cloud of gas. This had caused him to reconsider his assumption "that gas clouds were simply star clusters too far beyond our galaxy to be 'resolved' by his telescopes." Now he began to question whether nebulae were gas clouds within the Milky Way, and whether there really were galaxies outside our own. "It was a decisive retreat from his most radical thinking about the size and origin of the cosmos." It may have been prompted by a conservative reaction against the atheism of the French Revolution after the declaration of war against France. Herschel's friend, the French astronomer Jérôme Lalande, had become an atheist, and in 1807 wrote, "I have searched through the heavens, and nowhere have I found a trace of God." Pierre Laplace, another atheist, used Herschel's own theory that nebulae were stars forming out of clouds of gas to posit a theory of creation that made divine intervention unnecessary. When Napoleon once told Laplace that he found no mention of God in his books, Laplace replied "I have no need of that hypothesis."

However, Herschel maintained his freedom to speculate, sometimes wildly, as when he posited that the interior of the sun was cool and inhabited by intelligent beings. He also continued to believe that the moon was inhabited and "his disapproved of God-hunting within the galaxy," rejecting the notion that the fire of the sun was in fact that of the biblical hell. Other scientists suffered from the reaction against atheism, such as Joseph Priestley, whose library was destroyed by a Birmingham mob in 1794. Some even found visiting Herschel's observatory a religious experience, such as Joseph Haydn, who credited a visit to Herschel with inspiring his oratorio The Creation. 

Herschel's interest in the sun produced not only wild speculation, but also a significant discovery. In 1800 he did series of experiments with thermometers that demonstrated higher temperatures outside the visible spectrum, in short, he had "discovered the presence of infra-red light." Joseph Banks predicted that this would be a more important discovery than that of the planet Uranus. It also attracted the attention of the young Humphry Davy.

This marked a decisive advance on Newton's famous optical experiments with the prism, and implied a hitherto wholly unsuspected power in nature. It would also eventually lead to a decisive breakthrough in stellar astronomy in the twentieth century. 

During wartime Herschel was commissioned to produce a spy telescope to be mounted on Walmer Castle in Kent to watch for a French invasion fleet. But in July 1802, during the Peace of Amiens, he and his wife visited Paris where they met Napoleon, with whom he had a rather awkward conversation during which the future emperor proclaimed that astronomy "gave proof of an Almighty Wisdom." Knowing that Laplace, Napoleon's chief scientific adviser, was an atheist, Herschel thought Napoleon was a hypocrite. 

Ten-year-old John Herschel, who had accompanied his parents to France, fell ill on the way back. He was nursed back to health by his Aunt Caroline, to whom he became close -- "it was she, as much as his father, who inspired in him an early passion for science and astronomy." He had been sent to Eton when he was eight, but Caroline saw how unhappy he was there and was delighted when Mary saw her son knocked down in a boxing match with an older boy and decided to bring him home to be privately tutored.

In a paper in 1802, William began to speculate on the relationship between space and time, noting that "A telescope with a power of penetrating into space, like my 40  foot one, has also, as it may be called, a power of penetrating into time past." Other observations were equally unsettling to the layman, such as the notion that sunspots, because they had an effect on the Earth's temperature, "could be related to the price of wheat," and therefore have political consequences. Or that not only did the planets revolve around the sun, but the solar system was orbiting around the center of the Milky Way, which was itself moving through space. He also continued to develop the idea that the universe itself was evolving, and that the reason the nebulae he had observed were different shapes was that they were in different stages of development.

These shapes, Herschel argued, were not different because they had been created differently, like different species. They were different simply because their stages of development in what he called "sidereal time" (meaning stellar time) had reached different points. He was suggesting the inescapable idea of evolutionary youth and age in the universe. 

Copernicus had dethroned the Earth from the center of the universe. Now Herschel had gone so far as to remove even the Milky Way from the center.

Herschel's ideas and discoveries were picked up by the younger generation of Romantic poets. Byron visited him in 1811 and was astonished "when I viewed the Moon and Stars through Herschel's telescope, and saw that they were worlds." Keats used Herschel's discovery of Uranus as a central trope in his sonnet, "On  First Looking Into Chapman's Homer": 

Then felt I like some watcher of the skies
When a new planet swims into his ken 

It's a depiction of the moment of discovery as "a moment of revelation into the idea of the unbounded, the infinite. In the case of Herschel's sighting of Uranus, Keats's word 'swims' is brilliantly evocative, because of its sensse of new life and movement." Keats described a "Eureka moment," which Herschel's meticulous observation hadn't really been, though Herschel would later describe it that way. "Herschel in the end may have remembered that night exactly as Keats imagined it." In 1813, Thomas Campbell encountered the seventy-four-year-old Herschel  on vacation in Brighton.

Herschel completely perplexed the poet by remarking that many distant stars had probably "ceased to exist" millions of years ago, and that looking up into the night sky we were seeing a stellar landscape that was not really there at all. The sky was full of ghosts. "The light did travel after the body was gone." After leaving Herschel, Campbell walked onto the shingle of Brighton beach, gazing out to sea, feeling "elated and overcome." He was reminded of Newton's observation that he was just a child picking up shells on the seashore, while the great ocean of truth lay all before him.