In his Mizar–Alcor paper, Bond anticipated the advent of the astronomical sub-field known as photographic photometry by exploring the means to deduce a star’s brightness from the area of its circular image on the camera plate. His comparative study of the bright stars Vega and Arcturus likewise heralded the future of stellar astronomy. Although these two stars appear almost equally bright to the eye—in astronomical parlance, they have the same magnitude—Bond noticed that bluish-white Vega registers much more strongly on the blue-sensitive photographic plate than reddish-orange Arcturus. Bond asserted that a photographically determined magnitude gives a more objective and consistent measure of a star’s brightness than one derived by eye. In fact, astronomers would come to quantify a star’s subjective color by computing a color index—the numerical difference between the star’s visual and photographic magnitudes.
The Moon, planets, and stars were relatively easy to photograph using the wet-collodion process; more challenging were celestial objects like comets and nebulae, whose light is spread out over a patch of sky. The appearance of Donati’s comet in 1858 presented an opportunity to test the camera’s potential on a diffuse cosmic body. On September 28, Bond and Whipple succeeded in photographing the head of Donati’s comet with a six-minute exposure; however, the comet’s faint, diaphanous tail defied the camera. Bond instead sketched the comet by hand. (The night before Harvard’s telescopic attempt, William Usherwood, an English commercial photographer, secured a small-scale picture of the comet using a stationary tripod-mounted camera.)
Starting in the late 1850s, Bond published a series of papers that focus less on the photographic particulars of his new observing program, and more on the mathematical elements of extracting—and evaluating—measurement data from wet-collodion plates. He presented direct comparisons of photographically derived double-star measures with those obtained by eye: there was no discernible difference between the two. He highlighted the benefit of collecting the raw data on photographic plates at night, and inspecting them during the day. No more tedious manipulation of the micrometer eyepiece in the half-dark, no more writing down numbers in the shivery cold. The objectivity of the photographic plate, in Bond’s view, reduces errors that accompany the challenging environment of visual observing.
In a prescient take on modern institutional astronomy, George Bond envisioned a worldwide network of immense, mountaintop telescopes, each one equipped with a camera. These elevated instruments would be less burdened by the atmospheric turbulence and too-frequent cloudy nights that afflict sea-level observatories. In an 1859 paper, Bond exhorts that the “surface of the globe must be explored for the favored spots where a perfectly tranquil sky will afford the desired field for celestial exploration. If these were occupied, and faithfully improved, the fruits of the enterprise would be beyond all computation rich and interesting.” Larger telescopes were essential, Bond added. Telescopes three times the aperture of Harvard’s fifteen-inch refractor could be built without delay, if the money could be found. In the near future, wet-collodion plates would be passé, replaced by a soon-to-be-invented chemical process far more sensitive and easier to apply. Bond summed up his passion to William Mitchell in 1857: “There is nothing, then, so extravagant in predicting a future application of photography to stellar Astronomy on a most magnificent scale.”
George Bond’s evangelical fire about scientific photography found its counterpart in England with Warren De La Rue’s almost simultaneous return to celestial imaging. In September 1857, De La Rue renewed his campaign to photograph the Sun, Moon, and planets. His old reflector telescope, now fitted with a high-precision mechanical drive, had been installed in a two-story observatory on his new estate at Cranford, some fifteen miles west of London. The telescope, perched atop a fifteen-feet tall pier, occupied the building’s second story; a fully equipped photographic laboratory occupied the space below.
With its integrated darkroom, De La Rue’s observatory was the first to explicitly acknowledge the new role of photography in astronomy. Here, the telescope and the human eye serve as mere adjuncts to the camera, which captures the latent celestial image, and to the darkroom below, where the image is chemically revealed. Comfortably nestled on a private estate, the modest structure of brick, wood, and copper was the forerunner of industrial-scale observatories to come.
De La Rue’s facility also highlighted a noteworthy difference between visual and photographic observation. If possible, serious visual astronomers sit while observing, to best steady themselves while peering into the eyepiece. Breathing is periodically suspended, sometimes to the bursting point, to avoid fogging up the eyepiece lens. The importance of enforced stillness is not to be underestimated: William Cranch Bond designed an upholstered, mechanized observing chair for Harvard’s refractor that rode on rails around the instrument and cranked up or down to best situate the observer at the eyepiece. (Soften its edges, splash it with color, and Bond’s astro-mechano-chair would look right at home in a Dr. Seuss book.)
Warren De La Rue’s observatory at Cranford, as depicted in the British Journal of Photography, 1868.
De La Rue typically stood high on a stage near the focus of his Newtonian telescope, manipulating his photographic equipment while fine-guiding the telescope. Unlike the silent, motionless contemplation of a celestial object by eye, photographic observation requires frequent, active engagement with a host of chemical and mechanical necessities. Absent is the instant gratification of a direct visual sighting; the payoff is delayed until the plate is developed.
De La Rue’s upgraded telescope drive proved itself equal to the demands of photographic astronomy, keeping a star on the crosshairs for up to a minute. Of course, De La Rue knew that the Moon doesn’t move precisely in synchrony with the stars; it has its own orbital velocity around Earth. Therefore, he added a speed control to the telescope drive, slowing the instrument just enough to follow the Moon. (In fact, the Moon’s movement in the sky is more complex and sometimes required a periodic nudge of the telescope.)
By altering the preparation and development of the plates, De La Rue was able to take direct, wet-collodion negatives, which provided finer resolution than his direct positive plates from 1852. (The silver particles that comprise the image are larger on the positive plate than on the negative plate.) With improvements in collodion-plate sensitivity, De La Rue could now produce crisp images of the Moon in as little as three seconds. However, he learned that there was a practical limit to how far he could push the chemical responsiveness of his plates: not only did they tend to fog before being exposed, but spurious “stars” appeared on them as silver particles spontaneously precipitated out of the collodion.
In 1859, De La Rue delivered a lengthy address on celestial photography at the annual meeting of the British Association for the Advancement of Science. Unlike George Bond’s brand of advocacy, which was rooted in the research potential of the technology, “the man with the oil-can,” as De La Rue called himself, emphasized his working methods. The lecture was a primer on how to apply the camera to the telescope, with sufficient detail that colleagues need not just admire photography from afar, but could actually try it out. But he cautioned them: “[N]o one need hope for even moderate success if he dabbles in celestial photography in a desultory manner, as with an amusement to be taken up and laid aside.”
The text of De La Rue’s presentation has all the procedural complexity of a Latin Mass: how to clean the glass plate, how to hone the plate’s edges, how to mix the silver nitrate bath, how to prepare the collodion, even how far the water faucet must extend over the sink basin. De La Rue treats each plate with a solemnity normally reserved for a holy relic. His photographic laboratory is an 1850s version of a modern industrial clean room. Sanitary agents abound: tripoli powder, spirit of wine, liquid ammonia, alcohol. Hands are washed with a frequency that would delight an obsessive. Dust and lint are banished. Every working liquid is filtered through paper, then filtered again. De La Rue told the assembled scienti
sts with pride, “I have never any failure attributable to a dirty plate.”
De La Rue’s best lunar images—about an inch across on the original negative—could stand enlargement to an unprecedented eight inches. These paper prints were so fine-grained that inspection with a strong magnifier revealed lunar features in the image that were as small as a thousandth of an inch. Compared to the exquisite photographs, hand drawings began to seem quaint and unscientific, more impressionistic than realistic. In the succeeding years, De La Rue displayed enlargements of the Moon as wide as three feet, as well as a series of striking three-dimensional stereoscopic images of the globular Moon in space—“as if a giant with eyes a thousand miles apart looked at the Moon through a binocular,” in the words of John Herschel. De La Rue gained a powerful ally in Astronomer Royal George Airy, who acknowledged that his lunar photographs were much more accurate that any map or hand-drawing. (Airy’s interest in photography was more restricted than De La Rue’s or Bond’s: he viewed photography exclusively as a way to remove human bias from the kind of work done at the Royal Greenwich Observatory—positional astronomy and transit timings—not as a tool of discovery or exploration of the physical properties of celestial bodies.)
Wet-collodion photograph of the full moon by Warren De La Rue, as featured in John Nasmyth’s book, The Moon, 1874.
Among the pressing astronomical issues of the era was the nature of solar surface activity: what it might reveal about stellar physics and whether it influences the atmospheric and magnetic environment of Earth. In particular, there was need to investigate the observation by German amateur astronomer Heinrich Schwabe that sunspots wax and wane in an eleven-year cycle. Even before Schwabe’s discovery, John Herschel advocated daily visual monitoring of solar conditions, a proposal he renewed in 1854, but with the application of photography. The British Association for the Advancement of Science entrusted Warren De La Rue with the design and construction of a telescope to be dedicated to the project. Funded by a grant from the Royal Society, De La Rue’s “photoheliograph” was installed at Kew Observatory in 1858 and operated there, with few interruptions, until 1872.
The Kew telescope, a refractor, was just over four feet long, with an aperture of 3.4 inches, and featured a specialized lens that focused the visual and photographic rays to nearly the same plane. (Like daguerreotypes, collodion plates were more sensitive to blue and violet colors than to yellow and red.) A major challenge was the Sun’s overwhelming brilliance: only the shortest-duration exposures would render usable images. For the rapid-fire shutter, De La Rue conceived of a lightweight metal plate with a slot cut into it, tensioned by a rubber band and restrained by a thread. The shutter was actuated by burning the thread with a lighted taper. (Later it was simply severed with scissors.) The accumulated photographs helped form the database that led to eventual confirmation of Schwabe’s proposed sunspot cycle.
The eclipse of July 18, 1860, offered a timely opportunity to test the worth of wet-collodion photography. There had been a handful of passable daguerreotypes of solar eclipses; however, the technology was too slow to obtain a sequence of images showing the progression of the event. Nor had it captured ephemeral phenomena seen by eye surrounding the Moon’s limb during the brief minutes of totality. Visual observers disagreed about the form and nature of these features. English astronomer Francis Baily laid out the issue in an 1846 report about an earlier eclipse: “The accounts [of the corona and prominences] . . . are by no means satisfactory, since they are discordant in many particulars; [especially] the loose description that has been given of them, either by the observers themselves, or by those who drew up the accounts and perhaps did not fully comprehend the intention and meaning of the authors. The difficulty is also very much increased from the want of drawings to represent the exact appearances seen; which are always more readily understood by this method, than by any verbal description.”
With the indictment of hand sketches and verbal descriptions, English astronomers mounted an expedition to Spain to photograph the 1860 solar eclipse, and perhaps, to settle various controversies about eclipse-related phenomena. Among the participants were Warren De La Rue and a team of assistants, who had packed up the Kew photoheliograph and brought it to the Spanish village of Rivabellosa. There it was set up in a purpose-built shack with an attached darkroom. In fact, most of the expedition members were visual observers; even De La Rue brought along his sketch pad as a backup.
The photographs of the eclipse were completely successful, capturing a variety of luminous features that extended beyond the Moon’s obscuring limb. Among these were the mysterious “red flames,” or prominences as they are now called. Astronomers were split about the origin of the prominences: Are they fiery emissions from the Sun or volcanic eruptions from the Moon? (At the time, prominences could be seen only in the diminished glare of a solar eclipse, leading to uncertainty about their origin.)
A single photograph cannot answer this question, for it depicts only the superposition of the solar and lunar disks at a given instant; there is no sense of the crucial third dimension—the distance to the prominences. However, the sequence of De La Rue’s photographs showed clearly that the Moon gradually covered and subsequently uncovered the prominences, which remained fixed relative to the Sun: prominences originate in the Sun. The conclusion was affirmed when De La Rue traveled to Italy to inspect collodion plates taken by Angelo Secchi of the Vatican Observatory, who had photographed the eclipse from a site about 250 miles away. If astronomers harbored any doubt about the potential utility of celestial photography, here at least was one counterargument: it had resolved a scientific dispute.
In extracting quantitative data from the eclipse pictures—the size of the prominences, relative positions of the Sun and the Moon, and the like—De La Rue first had to determine whether the collodion plates were uniform. The flexible collodion layer might shrink or ripple on the glass, rendering any position or length measurements suspect. De La Rue assessed the stability of the collodion over a year’s time and concluded that there was no detectable shrinkage. He also proved, by taking hundreds of photographs of the identical scene, that cardinal points on successive plates differed by less than a thousandth of an inch. Collodion photographs could indeed be trusted for quantitative measurements in astronomy. De La Rue’s final report on the eclipse of 1860, including the resolution of the prominence issue and his various detailed measurements, was hailed by the astronomical community and served as a model for subsequent photographic eclipse studies. Two years later, he received the Gold Medal of the Royal Astronomical Society in recognition of the groundbreaking nature of his work.
Photography, once subordinate to the astronomer’s eye, was positioning itself to become a catalyst for a new means of discovery. To forward-thinking proponents like George Bond and Warren De La Rue, the design of observational astronomy verged on a dramatic rearrangement: What matters to the photographic astronomer is not what is seen through the telescope, restricted to an individual viewer’s perception; it’s what is recorded on the camera plate—“the retina which never forgets,” De La Rue called it—which is available for inspection by all. The technology intrigued professional astronomers, but with few exceptions, these seasoned skywatchers were not ready to stake their advancement in the field on a nascent method. Further refinement would have to come from those with sufficient time, skill, and means: self-sustaining amateur scientists outside of academic institutions.
Chapter 7
THE ARISTOCRAT AND THE ARTISAN
I take great pleasure in bringing to your notice, the workmanship of Mr. Fitz, as he is an American and a self-taught artist, who places within our reach at home, those instruments which heretofore have been obtained from abroad, at a great cost.
—Lewis M. Rutherfurd, astronomer, 1848
LEWIS MORRIS RUTHERFURD was the quintessential nineteenth-century amateur scientist, who crisscrossed the boundaries between practitioner and patron, scholar and craftsman, theorist and
experimenter. Born into great wealth, elevated into stratospheric wealth (through marriage to a Stuyvesant), Rutherfurd could have spent his life and his fortune toward any end he might have desired. Yet it would be a mistake to define the man by the obligatory yacht; elite racket club; or slew of senators, justices, governors—even a signer of the Declaration of Independence—dotting his patrician pedigree. Rutherfurd possessed, according to one scientific colleague, an “almost shrinking modesty” and a “singular absence from all ostentation.”
After graduating from Williams College in 1833, at age eighteen, Rutherfurd studied law with William H. Seward, later Lincoln’s Secretary of State, and George Wood, whom Daniel Webster regarded as one of the country’s finest legal minds. Rutherfurd passed the bar exam in 1837, then practiced law in New York City for the next twelve years, before retiring to Europe in response to his wife’s frail health. While in Florence, he renewed his latent interest in science—he had studied physics at Williams, even cobbled together a telescope “from spare parts found in a lumber room”—by studying with the optics expert Giovanni Battista Amici.
Lewis Morris Rutherfurd.
Upon his return to the United States in 1856, Rutherfurd erected a small astronomical observatory and workshop behind his mansion in fashionable lower Manhattan, “189 feet N.W. from Second Avenue and 76.3 feet N.E. from Eleventh Street.” The tasteful, brick-faced structure was some twenty feet in diameter, with a revolving dome and an attached chamber that housed a transit telescope. (A retail–residential complex occupies the site today.) The urban setting was hostile to astronomy. The lower expanses of the night sky were eclipsed by adjacent buildings and the towering willows of nearby St. Marks Cemetery. The air seemed ever-infused with dust and scattered light. The ground trembled every time a freight wagon rolled by. Rutherfurd brooded over these environmental intrusions. Yet his interests lay more in the engineering aspects of instruments than in astronomical discovery, a line of inquiry more amenable to his city-bound technological oasis.
Starlight Detectives Page 9
