Starlight Detectives

by Alan Hirshfeld

  The thirteen-inch hybrid refractor was a complete success. In 1871, Rutherfurd secured photographs of the Sun’s surface that revealed the never-before-seen mottling known as “granulation.” (Rutherfurd neglected to announce the result until its independent discovery seven years later by French astronomer Jules Janssen.) Despite the renown of his solar and lunar work, Rutherfurd persisted in his efforts to prove the viability of celestial mapping, or astrometry, by photographic means. Throughout the 1870s, he designed and built a series of increasingly sophisticated table-top micrometers to measure relative star positions from exposed plates. His exhaustive study of the stability of collodion films neutralized critics’ claims that archived photographs shrink or warp over time, rendering them useless for measurement.

  Over the coming decades, Rutherfurd’s most vocal champion, astronomer Benjamin Apthorp Gould, extended the photographic study of star clusters to the Southern Hemisphere. Gould admitted that reduction of the accumulating pile of exposed plates would entail hundreds of hours of laborious measurement. Yet, compared to visual reckoning at the telescope, he declared the task eminently sensible: “[I]nstead of being restricted to favourable nights, at favourable seasons, and painfully made by the astronomer in inconvenient postures and under all the attendant disadvantages, [photographic measures] may easily be performed at any time and place, even in another hemisphere, with all the convenience and comfort which the nature of the case admits, and subject to indefinite repetition. Sufficient material to occupy all the energies of an astronomer for a year or more may thus easily be collected in a single night and reserved for subsequent study.”

  In 1866, Gould announced to the National Academy of Sciences that photographically derived positions of stars in the Pleiades were in precise accord with those derived visually by the legendary German observer Friedrich Bessel. A follow-up study of the Praesepe cluster was equally positive. Gould postponed formal publication of his results for some two decades in deference to Rutherfurd, who planned to publish his own report of his measurement techniques. He never did, confiding to a fellow astronomer that he did not want to “rush into print.” As ill health overtook him later in life, Rutherfurd donated all of his plates and measuring machines to Columbia University, where the task of measurement and analysis was completed by faculty and graduate students. The full record of star cluster positions was finally published in a series of volumes during the 1890s.

  Overall, in the two decades following his first lunar photograph in 1858, Rutherfurd recorded 435 plates of the Moon, 349 plates of the Sun and the solar spectrum, and 664 plates of star groups and clusters, including fifty-four images of the Pleiades. Scientific American hailed him “by far the most distinguished private scientist in the United States.” In fact, Rutherfurd was more an emissary from the world of engineering than a “pure” research scientist. Beauty was to be found in the refinement of an apparatus, in the scientific utility of a method. A picture’s worth was to be judged, not by an arm’s-length aesthetic assessment, but by a microscopic, pointillist’s inspection of the images. The universe, to Rutherfurd, was a test bed for technological innovation.

  Perhaps the ultimate sign of Rutherfurd’s acclaim was the letter he received in 1886 informing him of his election to the French Academy of Sciences. The envelope was addressed simply:

  Lewis M. Rutherfurd, Astronomer

  New York, N. Y.

  Chapter 8

  PASSION IS GOOD, OBSESSION IS BETTER

  When Henry and Anna Draper rode home in their carriage from Hastings-on-Hudson to their house at Dobbs Ferry on the night of the first of August, 1872, they had just obtained the final proof, the demonstrably objective evidence, that one star . . . more than a million times further away than the sun, was made of the same atoms that are most abundant in man.

  —E. L. Schucking, “Henry Draper: The Unity of the Universe,” 1982

  IN 1856, WHILE LEWIS RUTHERFURD was sighting the heavens from his new downtown observatory, fellow New Yorker Henry Draper sat hunched over a microscope, taking pictures of frogs’ blood cells for his medical school thesis on the spleen. Son of renowned scientist–scholar John William Draper, who first photographed the Moon from a rooftop on Washington Square, it’s no surprise that Henry chose to record the diminutive images with a camera instead of a pencil. He had mastered the art of micro-photography at thirteen, preparing illustrations for his father’s forthcoming book on human physiology.

  Henry spent his formative years in a lofty, upper-middle-class atmosphere of culture and scientific inquisition, established by his parents and stoked by five studious siblings. John Draper was a literary dynamo, weighing in on subjects in science, history, sociology, and philosophy. He courted controversy, whether his Darwinian-inspired lecture on the intellectual development of Europe, at the 1860 Oxford evolution debate, or his 1874 book, History of the Conflict between Religion and Science, which was banned by the Catholic Church. His “Appeal to the People of the State of New York, to Legalize the Dissection of the Dead,” in 1854, led to legislation that lifted medical school anatomy classes out of the shadows.

  Of the six children, Henry was his father’s favorite. Henry’s niece, Antonia Maury (who would become an astronomer at Harvard), recalled that when John and Henry conversed, “the rest sat silent. For it was well known that everything they said was too important for any word of it to be lost. To his father . . . Henry was the perfect foil, his dark eyes flashing electrically over the latest discoveries in physics or astronomy, or when relating some humorous incident, they brimmed with laughter to the point of tears.”

  John Draper was omnipresent in Henry’s development as a scientist. The three-year-old Henry might well have been present in 1840 when his father photographed the Moon from an upstairs room or when he posed his Aunt Dorothy for her now-famous portrait. Harper’s Weekly reported that Henry “had for a companion, friend, and teacher, from childhood, one of the most thoroughly cultivated and original scientific men of the present age, who attended carefully to his instruction, and impressed upon him deeply the bent of his own mind in the direction of science. . . . Henry Draper inherited not only his father’s genius, but his problems of research.” The magazine regarded the Drapers as a latter-day incarnation of the famous father–son team of William and John Herschel. “On one side was the sincerest filial devotion, respect, and admiration,” astronomer Charles A. Young noted in 1883, “on the other, paternal pride and confidence; on both sides, the warmest affection, and perfect sympathy of purpose and idea.”

  Two years into his undergraduate studies at the University of the City of New York (now New York University), Henry Draper transferred to the medical school, which his father had cofounded. Having breezed through the entire medical curriculum by 1857, the twenty-year-old Draper found himself fully trained, yet too young to receive his degree. Instead, he embarked with his older brother John Christopher, a physician and chemist, on a year-long scientific and recreational tour of Europe.

  Henry Draper.

  In Dublin that August to attend the meeting of the British Association for the Advancement of Science, Draper accepted Lord Rosse’s invitation to view the famous Leviathan of Parsonstown, largest telescope in the world. What the Leviathan lacked in refinement, it more than made up for in immensity and sheer boldness of ambition. Its yawning, six-foot aperture funneled a veritable torrent of cosmic light into the eye, allowing astronomers to see celestial nebulae invisible through smaller instruments. This was a telescope designed to push back the frontiers of deep-space observation. Yet Henry Draper was struck not only by the instrument’s immensity and its vivid images of the night sky, but by the intricate machines that Lord Rosse developed to forge, grind, and mount the two-ton, solid-metal mirror. Schooled in the earthbound realm of human disease and experienced only in the cramped world of the microscope, Draper saw a totally different path unfold before him. He would join the ranks of those who directed their scientific attentions upward. Like Rosse, he w
ould build his own metal-mirror reflector when he returned home. The specifications of his telescope were simple: it would be the largest reflector in America; and, unlike the creaky, pulley-driven Leviathan, its optical system and mount would be tailored to celestial photography.

  By the time Henry Draper and his brother returned to New York in 1858, the post-daguerreotype era in observational astronomy had already begun. George Bond, at Harvard, and Warren De La Rue, in England, were taking unprecedented wet-collodion pictures of the Sun, Moon, and stars. Even so, the photochemical process remained too inefficient and telescope drives too inaccurate for most astronomers to acknowledge photography’s potential for discovery. Its perceived merits during this nascent phase lay in its permanency, its reproducibility, and, most of all, its objectivity.

  The human hand, guided subjectively by the eye and the mind, and hindered by darkness and discomfort, had produced drawings of celestial objects for centuries. Astronomers like John Herschel and George Bond were known for their artistic caliber. But many telescopic observers lacked the skill to render on paper more than a stick-figure equivalent of the vision in the eyepiece. Charles Piazzi Smyth, Astronomer Royal of Scotland, acknowledged his colleagues’ misguided impulse to heighten or otherwise embellish what they saw: “No astronomical drawing ought, however, to be invaded by any such device for procuring a general effect; no vague expression or semblance of that which exists must be allowed to take the place of painstaking, accurate, and detailed delineation.”

  The actuality of heavenly bodies was subsumed to various degrees by each artist’s imagination and skill. Whatever Lord Rosse spied through his mighty Leviathan telescope, the published sketch of his self-described Crab Nebula resembles more a ragged pineapple than its namesake crustacean. For an 1867 portrayal of the Orion Nebula, Rosse turned over his pencil to a local draftsman. Harvard College Observatory and the U.S. Naval Observatory called upon the gifted pastel artist Etienne Leopold Trouvelot well into the wet-plate era of photography. If not the most accurate depictions of celestial sights, Trouvelot’s are certainly the most beautiful. (Trouvelot is less favorably remembered for his introduction of the gypsy moth to North America.)

  A thorough hand-rendering of, say, a lunar landscape or a wispy nebula required many nights at the telescope—peering, sketching, adding, refining. A single camera exposure, in principle, could accomplish the same task in minutes. A library of such plates would comprise a permanent, unbiased chemical archive of the astronomical realm. Photographs from different eras might reveal subtle changes unseen by the astronomer’s eye: volcanic eruptions on the Moon, the gravitational swirl of a gaseous nebulae, snail-paced rearrangements of the members of a star cluster. Dreams all, in the late 1850s when Henry Draper set to work on his telescope.

  During September 1858, Draper crafted a reduced-scale version of Lord Rosse’s mirror-grinding machine, whose oscillatory strokes would impart the proper concavity to a speculum-metal disk. The following November he cast a fifteen-inch-wide, two-inch-thick slug of the finest Minnesota copper and Sumatran tin, weighing 110 pounds. Then commenced a seemingly interminable cycle of incremental grinding, polishing, and optical testing. Unlike Lord Rosse, who ran something of a feudal estate, Draper did not relegate work to subordinates (not that he could afford to); he carried out the complex engineering himself, always with minute attention to detail.

  Progress on the telescope was glacial: Draper’s passion for astronomy was subservient to the need to earn a living. In 1859, he joined the medical staff at Bellevue Hospital, but soon left to become professor of physiology at his alma mater, New York University. By all accounts, he was a popular teacher, committed to the education of his students. The NYU Quarterly reported:

  His lectures are so interesting and absorbing to his hearers, that the question of order, which in some recitation-rooms assumes large proportions, is hardly even thought of with him. After class, an eager group surrounds him; and every tap by inquiring students is followed by a rich stream of information from a mind whose varied treasures always lie at instant command.

  By 1860, almost a year and a half after it had been cast, the fifteen-inch speculum was nearing completion. On several occasions, Draper had mounted it in a wooden tube and tested it out on the night sky, with mixed results. The correction process was a vitreous Whac-a-Mole: every time he polished out a defect in the mirror’s curved surface, another defect popped up somewhere else. On a chill day in February, Draper arrived to find the fragile mirror fractured: water had intruded into its support case during the night, frozen, and heaved. He would have to start over. Draper made no mention of the accident in a midsummer report to the British Association at Oxford; a replacement mirror would be in service soon enough. Presumably, he shared the stoic attitude of many telescope enthusiasts, for whom failure was an inevitable tax levied against progress. When his own telescope lens broke at a remote station in Argentina, astronomer Benjamin Gould remarked, “Lamentations being useless I did the best that I could.” Gould secured the glass pieces in a frame and continued his observations.

  John Draper might have been three thousand miles across the Atlantic at the time, but he was always in the loop of Henry’s activities. He wrote in June 1860 with urgent news. He had told the English astronomer John Herschel of his son’s travails with metal mirrors. Herschel pressed Henry to abandon the fraught speculum-telescope design that had endured since the time of Isaac Newton. Instead, he should construct a mirror of silver-coated glass, like the ones only recently developed by Léon Foucault in Paris and Carl August von Steinheil in Munich. (Evidently, Henry had missed Foucault’s lecture on glass-mirror telescopes at the 1857 British Association meeting he had attended in Dublin.) Foucault had also published a report describing his so-called knife-edge test, an innovative optical procedure that reveals microscopic defects in a mirror’s curvature. For the first time, telescope makers could assess the quality of an astronomical mirror in the workshop.

  Casting back some 90 percent of incoming light, silvered-glass mirrors were more reflective than their speculum-metal counterparts, which never exceeded 75 percent. The enhanced reflectivity would no doubt shorten photographic exposure times. Glass was also easier to work than the brittle speculum metal alloys, which—as Draper knew from experience—were apt to split under pressure or cold. The composition of the glass was almost immaterial; a glass mirror’s reflective element lay, less than a hair’s thickness, on its surface. And, inch for inch, a glass mirror was a mere one-eighth the weight of a metal mirror: Draper’s fifteen-inch reflector would shrink from a hefty 110 pounds to less than twenty.

  Draper took Herschel’s advice. Based on what meager information he could acquire from Europe, he spent the next year experimenting with glass-silvering techniques, achieving success in late 1861 with a process by English chemist John Cimeg. The completed mirror, whose substrate was a piece of glass originally destined for a ship’s deadlight, was fifteen and a half inches in diameter. The thickness of its glistening silver coat he estimated at about 1/200,000 of an inch. Within three years, Draper had ground, polished, and silvered more than a hundred glass mirrors, ranging in diameter from a quarter-inch to nineteen inches.

  The delicate grinding and polishing process was mechanized, in suitable Victorian-era fashion. Draper and his younger brother Daniel took turns on the treadmill-powered rough-grinding machine, sometimes walking the equivalent of ten miles during a five-hour shift. Hearing that the two men had (unsuccessfully) tried to run dogs on the track, their amused father cautioned his daughter Antonia to refuse if they came for her. With its gnashing gears, articulating rods, and incessant grate of abrasive upon glass, the workshop must have been a raucous environment. Yet Draper seems to have been immune to the mill-like assaults on his senses: “It becomes a pleasant and interesting occupation to produce a mirror.”

  Draper was acutely sensitive to environmental factors that afflict the final shape of the mirror: “A current of cold air, a gleam of sun
light, the close approach of some person, an unguarded touch, the application of cold water injudiciously will ruin the labor of days. . . . [T]he amateur can only be advised to use too much caution rather than too little.” He found that a perfectly formed reflection of an illuminated pinhole flared, even bifurcated, from the warmth of his hand held at the back or the edge of the mirror. The imperceptible warp of the glass lingered after he removed his hand. If the mirror was polished in this distorted state, the warp became permanent, and the highly magnified images of stars were ruined.

  Anticipating his telescope’s completion, Draper hired a carpenter to erect a small stone-and-wood observatory on the grounds of the family estate at Hastings-on-Hudson, twenty miles north of New York City. (John Draper supplemented his income by leasing out cottages on the estate, which is now a museum and archive.) The building was topped with a lightweight, sheet-metal-clad dome, sixteen-foot across, that could be rotated easily by one hand. Family friend Lewis Rutherfurd could only envy Draper’s rural observatory site. Into the distance, the slopes and summits were a rolling sea of trees, broken by the occasional house or clearing. “An uninterrupted horizon is commanded in every direction,” Draper enthused, adding that “often when the valleys round are filled with foggy exhalations, there is a clear sky over the observatory, the mist flowing down like a great stream and losing itself in a chasm through which the Hudson here passes.” In fact, the idyllic scene would prove less than ideal for celestial photography, once Draper evolved from a dewy-eyed amateur into a seasoned professional. It wasn’t long before he started to dream, as astronomers will, of remote mountaintops, swathed nightly in utter blackness and desiccated air, a truly hospitable home for a telescope.