Starlight Detectives

by Alan Hirshfeld

  When it came to fitting his observatory with a telescope, Rutherfurd opted to go local. Henry Fitz, the first American telescope maker of consequence, ran a small shop on Fifth Street, six blocks from Rutherfurd’s home. Like Rutherfurd, Fitz had been a precocious tinkerer, concocting his first telescope at age fifteen with a lens scavenged from a pair of eyeglasses. Largely self-taught, he read voraciously about science and mechanics. In 1837, at age twenty-nine, Fitz shunted aside his lucrative lock-making business to help a friend grind and polish a telescope mirror. The project swept him into a new career as an optician. Fitz honed his optical skills in 1839 during a four-month blitz through the workshops of England’s master instrument makers. However, he found the quality of English telescopes and raw optical glass not much better than those available back home. The supreme creations were produced on the Continent: telescopes from Germany, optical glass from France.

  During the early 1840s, Fitz pursued his off-hours optical hobby while running a successful daguerreotype studio in Baltimore. One of his earliest lenses was fashioned from the sawed-off bottom of a flint-glass tumbler. An observing run in the autumn of 1844 with a friend’s German-made refractor—by the peerless optician Joseph Fraunhofer—tipped Fitz’s hobby into obsession. The making of an astronomical lens was no trivial venture. One London wag remarked, “Men have been known to go and throw their heads under waggon wheels, and have them smashed, from being regularly worn out with working an object glass, and not being able to get the convex right.”

  Fitz’s wife, Julia, recalled being awakened one night in January 1845, when her husband excitedly announced that he had crafted a telescope equal to those of his European rivals. “I was soon on the balcony with him,” she remembered, “and there sure enough was Jupiter with well defined disc, without a particle of stray light, clear and beautiful. . . . I never saw him in such a glow of enthusiasm, so perfectly radiant with happiness, as that night.”

  Before the year was out, Fitz shuttered the Baltimore studio and opened his telescope-making shop in New York City. The business was an immediate success, with a variety of individual and institutional clients clamoring for an American-made refractor. Fitz ran a lean operation, employing only two assistants and, eventually, his son Henry G. “Harry” Fitz. He was as intent as a high-end diamond dealer on securing a steady supply of high-quality optical glass, free of streaks, bubbles, and otherwise ruinous flaws. One visitor marveled at the transparency of the raw European crystal: so clear, he noted, that he could see through a sixteen-inch width as plainly as he could see through the air. Between 1845 and 1860, Fitz would produce 40 percent of all telescopes sold in the United States. In 1861, he would complete what was then the largest telescope in the country, a refractor of sixteen inches aperture; the buyer: Buffalo dentist William Vanduzee, who found neither money nor practicality a bar against indulging his daughters’ interest in the heavens.

  Henry Fitz.

  Having ordered several telescopes of increasing aperture, Lewis Rutherfurd became a regular in Fitz’s optical shop, absorbing everything he could about the art of lens grinding and figuring. Telescope makers were notoriously secretive about their methods. Yet Fitz evidently had no qualms about revealing his processes to Rutherfurd, whose scientific acumen complemented Fitz’s more intuitive approach. Even while Rutherfurd was in Europe, Fitz kept “Friend Rutherfurd” informed of his activities. His letters often overflow onto the envelope with arcane details of the optical business as well as neighborhood chit-chat. Across an ocean and a social divide, the two men bonded over the minutiae of abrasive powders, rivets, and bench tests, both striving toward the same end: technical perfection. In a letter dated November 12, 1849, Fitz tells of the birth of his second son, whom he and his wife named Lewis Rutherfurd Fitz.

  From the start, Rutherfurd was an ardent promoter of Fitz’s instruments. He closed an 1848 report to the American Journal of Science about a recent lunar eclipse with this encomium about his Fitz refractor: “My largest is an achromatic telescope, equatorially mounted, of six inches aperture and eight feet focus. The object-glass is the workmanship of Mr. Henry Fitz of this city, an optician of great skill and rising reputation. . . . [I]t has shewn me at one time last winter, the disk of Jupiter covered with small belts, in addition to the two usually seen, while two of his satellites were plainly seen projected upon the planet’s disk, followed by their shadows, which were as distinct as black wafers upon white paper.”

  Throughout much of 1856, Rutherfurd and Fitz labored side by side to sculpt an eleven and one-quarter-inch objective lens for the newly built observatory on Second Avenue. Just over fourteen feet long, the completed telescope excelled at high-magnification views of lunar and planetary surfaces. Yet it didn’t take long for Rutherfurd to chafe at the limits of visual astronomy. He was a Victorian-era “techie,” and always alert to the next innovation.

  As England’s Warren De La Rue had been spurred by Whipple and Bond’s 1851 daguerreotype of the Moon, so Rutherfurd found his own muse in the most recent series of wet-plate images from Harvard. In the spring of 1858, he fitted his telescope with a precision drive like the Great Refractor’s, and immediately began to photograph the heavens. His initial pictures, while comparable to those obtained by others, were, by his own exacting standards, a failure. His best photographs of the Moon could sustain only a five-times enlargement before lunar features lost definition. Nor did his plates surpass the human eye in “seeing” faint stars. Close-together double stars, which appeared as a pair of luminous points through the eyepiece, were cloaked in an oblong cocoon of light on the plate. Jupiter’s moons, visible to Galileo even in a lowly spyglass, eluded Rutherfurd’s camera entirely.

  Rutherfurd experimented with the preparation of the collodion, at one point bathing the plates in a grape-sugar solution to enhance their sensitivity. He tested various thicknesses of collodion and tried a host of variations in the development process. “The making of the best negative seems to be a matter of compromises,” he concluded. “We cannot have [light sensitivity] and fineness of detail at the same time.”

  The main culprit, Rutherfurd realized after a time, was not chemical, but instrumental. His telescope, like Harvard’s refractor, had been designed for visual observation, not for photography. He and Fitz had shaped the lens components so as to focus the rays of “eye-friendly” colors, such as green and yellow, to the same point. Shades of violet remained uncorrected: even on the clearest of nights, every star in the eyepiece appeared as a scintillating, whitish speck enveloped in a subtle corona of violet. The halo effect was hardly noticeable to the eye and did not diminish the aesthetic pleasure of peering at celestial objects.

  This same visual correction was problematic for celestial photography, whose wet-collodion plates—like the daguerreotype before it—were activated by violet light. Whereas the eye sees primarily the point-like core of a star’s image, the camera records only the out-of-focus, violet-triggered halo. (Naturally, the halo lacks color on a black-and-white plate.) Through trial and error, Rutherfurd concluded that the best focus for photography—the place inside the telescope where violet rays nominally converge—was seven-tenths of an inch behind the visual focus. Yet, to his chagrin, shifting the plate to this position yielded only modest improvement. In fact, nowhere along the telescope’s optical axis did the plate-activating violet rays perfectly unite.

  In 1859, Rutherfurd retrofitted his visual refractor with a succession of correcting lenses provided by Fitz. Surely, he believed, some lens or combination of lenses, inserted along the telescope’s light path, would impel all shades of violet to a common focus on the photographic plate. (In similar fashion, modern astronomers managed to sharpen blurry images formed by the Hubble Space Telescope’s misshapen primary mirror.) Two years of experimentation yielded only partial success: images near the center of the plate were crisp, but those toward the periphery remained indistinct.

  By late 1861, Rutherfurd had had enough. He abandoned the refrac
tor design entirely in favor of a mirror-based telescope, which is inherently free of chromatic aberration. But there was a downside. Stars look different in a reflector telescope than in a refractor. English amateur astronomer Andrew Ainslie Common described it this way in 1884: “If we look with a reflector at a bright star, the image is seen as a bright point of light, dazzling to the eye if the telescope is large, and we see rays or coruscations round it of an irregular shape that are never steady. . . . The image of such a bright star in the refractor is quite of another kind: it is seen as a small disk of light of sensible diameter surrounded by the well-known system of diffraction rings and outstanding colour. The disk of light, though small, has a different effect on the retina: it can be seen as a shape, pretty steady and free from too much dazzling glare.”

  In short order, Henry Fitz delivered a lightweight thirteen-inch-wide, ten-foot-long reflector telescope, which he and Rutherfurd strapped papoose-style to the tube of the main instrument. Rutherfurd’s frustration only mounted. The incessant tremors of the city kept the reflector’s delicately sprung mirror in a constant state of agitation, spoiling the photographic images. And unlike the refractor’s maintenance-free lenses, airborne moisture and pollutants attacked the mirror’s fragile reflective glaze. Every ten days, Rutherfurd had to remove the tarnished disk and perform a noxious resilvering procedure—“a labor,” he confided, “not to be contemplated with equanimity.” After just three months, Rutherfurd set the reflector aside.

  In his writings from this period, Rutherfurd refers to his visually corrected telescope lens (pejoratively?) as the uncorrected objective, revealing his photographic bias: the camera, not the eye, was to be the sole arbiter of image quality. Here emerges an evolving paradigm in astronomical observation. For centuries, the telescope had been considered an optical adjunct of the human eye; now commenced its gradual transformation into a photographic accessory. In essence, the telescope was reimagined by Rutherfurd as but a giant telephoto lens for the camera.

  Rutherfurd realized that his photographs would never come into crisp focus until he renounced the human eye’s longstanding hegemony over telescope design. The only way to take full advantage of photographic technology was to bypass the eye entirely and design a telescope exclusively for the camera. In such a telescope, the various shades of violet would all focus onto the plane of the photographic plate. That other colors were out-of-focus at this same location was immaterial, as these retinal-stimulating rays do not register on a violet-sensitive plate. Rutherfurd’s photographic refractor would be a radical departure from centuries-long tradition: it would be utterly useless for visual observing; nowhere along its optical axis could the eye see images in focus.

  Rutherfurd and Fitz turned their working partnership toward the iterative task of creating, testing, and correcting the new type of telescope lens. It was an arduous process: cutting and shaping the best pieces of optical glass that could be had; testing each attempt on an artificial star in the workshop, then on a real star in the night sky; smoothing out of rough patches on the glass surfaces, this last with bare thumbs and a sprinkle of wetted rouge abrasive. By 1863, with the U.S. Civil War in full blaze, Henry Fitz had telescope commissions coming in as fast as his modest workshop could handle. He was training his now-teenage son Harry in the lens-grinding craft and was building a house, with a workshop and top-floor observatory, down the block from Rutherfurd’s. In the works was Fitz’s most ambitious project to date: construction of an unprecedented twenty-four-inch refractor, for which he planned to sail abroad at year’s end to handpick the raw glass disks. The instrument was never realized: Fitz died on October 31, 1863, after a brief illness.

  Rutherfurd took on the young Harry Fitz as his new collaborator, simultaneously preparing him to lead his father’s firm (which he did for almost twenty years). They immediately resumed work on Rutherfurd’s photographic refractor. But what guide can be used to shape a lens whose focusing properties cannot be assessed by eye? That is, how can the crucial violet component of a star’s image be isolated so its best focus can be determined? Coincidentally, news had arrived only recently from Germany of a great scientific advance. Gustav Kirchhoff and Robert Bunsen had discovered that the Sun’s chemical composition could be deduced by spectroscopic analysis of its light. Rutherfurd realized that a star’s spectrum is precisely what he needed to test his photographic lens. A prism, placed at the nominal focus of the lens, will disperse starlight into a narrow spectrum, red at one end, violet at the other. The color at which the spectrum is narrowest is the one that has been brought into most vivid focus. The lens is repeatedly reshaped and retested until the violet segment of the spectrum is a virtual hair’s width across.

  In December 1864, Rutherfurd replaced the visual objective of his eleven and one-quarter-inch refractor with the photographic lens he and Harry Fitz had completed. The improvement was startling. Now that a star’s violet rays were sharply focused onto the plate, images formed some ten times faster than with the visual objective. A three-minute, wet-plate exposure recorded stars six times fainter than any previously impressed on a photographic plate, regardless of exposure time or telescope size. “The power to obtain images of the 9th magnitude stars with so moderate an aperture,” Rutherfurd notes in an 1865 article in the American Journal of Science, “promises to develop and increase the application of photography to the mapping of the sidereal heavens, and in some measure to realize the hopes which have so long been deferred and disappointed.”

  Rutherfurd’s prime targets were star clusters, whose relatively compact dimensions allowed them to be imaged onto a single plate. What better than a decades- or even centuries-long series of photographs to ascertain the relative positions—and possibly systematic movements—of a cluster’s stars? Such movements, if detected, might reveal the distance and the overall mass of the cluster, physical quantities otherwise difficult to obtain.

  Between 1865 and 1867, Rutherfurd took forty-five plates of the Pleiades and Praesepe star clusters with his photographic refractor. A decade earlier, astronomers struggled to image even a single star; Rutherfurd’s typical Pleiades plate captured around 175. So pinpoint-sharp were these star images that they could not be distinguished from motes of dust in the collodion itself. Rutherfurd was compelled to record two photographs on every plate: one long exposure, followed by a thirty-second, closed-shutter pause (during which Earth’s rotation slightly shifted the view), then a second, briefer exposure. The result: all of the star images appeared double, while the dust spots remained single.

  Despite its astrophysical promise, Rutherfurd’s hoped-for photographic revolution stalled. The majority of professional astronomers considered wet-plate photography to be an esoteric practice, more chemical manipulation than science, whose utility remained suspect. The photographic images of star clusters were viewed by researchers as representational art, not dissectible data.

  Although Rutherfurd’s star cluster photographs passed almost unnoticed, his lunar images fairly burst onto the scene. A two-second exposure of the first-quarter Moon, taken on March 6, 1865, was shown at meetings worldwide, reproduced in books, and sold as large-format prints. The editor of The Philadelphia Photographer raved: “[W]e are filled with mingled wonder, and awe, and admiration. . . . The attempts of De La Rue, Bierstadt Bros., and others have all been successful, but in no ways as successful as Mr. Rutherfurd.”

  Rutherfurd recounted that it was the preternatural stillness and transparency of the air that evening that allowed the crystal-clear image. Photographic pioneer Warren De La Rue agreed that the night must have been superb: “I have made many thousand photographs but never could get one like that and I don’t believe if Mr. Rutherfurd makes thousands more that he will ever get such another.” From their respective negatives, De La Rue could manage up to an eightfold enlargement before loss of definition, Rutherfurd more than twelvefold.

  Professional astronomers likewise marveled at the photograph’s aesthetic caliber; on the other
hand, they failed to accord it much scientific value. True, a vivid—and completely objective—pictorial record might reveal changes in the lunar landscape caused by, say, lava-spewing volcanoes or meteor impacts. Yet as crisp as Rutherfurd’s image was, it lacked the sharpness of a direct view through the best telescopes. The eye makes use of the rare instances when atmospheric turbulence subsides and the lunar surface snaps briefly into crystalline focus. The camera, even with an exposure of just a few seconds, is utterly democratic in recording all the jitters of the image. What appears as a jagged, rock-rimmed crater to the eye becomes, under a magnifier, a velvety, grayish circle on the photographic plate. (Think of a portrait by Vermeer as opposed to one by Renoir.) Rutherfurd had pushed wet-collodion imaging of the Moon to its very limit. It was not until the 1880s, and the emergence of a new photochemical process, that lunar photography resumed its advancement.

  In 1868, Rutherfurd replaced his eleven and one-quarter-inch photographic refractor with one of thirteen-inch aperture, whose visual objective could be adapted in minutes for photographic use by attachment of a screw-on supplementary lens. (The lens of the eleven and one-quarter-inch refractor broke in transit to a South American observatory. The thirteen-inch telescope, donated by Rutherfurd to Columbia University, was acquired in 2003 by antique telescope collector John Briggs.)