Starlight Detectives

by Alan Hirshfeld

  Whipple’s studio and display gallery occupied the upper floors of three adjacent buildings on Washington Street, Boston’s busiest commercial thoroughfare. Fitting out the premises to suit the opulent sensibilities of his mostly upper-class clients had cost him over $25,000. At the height of the business, he employed nearly forty people.

  Boston studio photography during the 1840s was a rough-and-tumble enterprise. Whipple proved to be something of a marketing impresario. He advertised incessantly, featuring his proprietary innovations, such as the steam engine he used to polish photographic plates, run an immense cooling fan for the comfort of clients, heat up cups of mercury, distill water, even revolve the gilded sunburst at the entrance of his establishment. (His catch-phrase: “Daguerreotypes by Steam.”) Whipple produced a Grand Optical Exhibition in Boston’s Tremont Temple, featuring projected views of Rome, Mexico, and Palestine, plus portraits of P. T. Barnum’s Swedish Nightingale, Jenny Lind, “thrown upon the scene as large as life.”

  If possible, Whipple’s seemingly boundless marketing energy was exceeded by his practical inventiveness. Through a clever optical enlargement scheme, he offered super-size photographs, among them the largest-ever print of a street scene, nearly five feet by three feet. He developed and patented the crystalotype process to generate, from a single glass negative, unlimited paper prints, which publishers could tip into books. He was first in the world, in 1846, to take a passable daguerreotype through a microscope—a ninety-minute exposure of a spider’s mandible. “By this most simple means,” Whipple writes, “it is in the power of every Dagerreotypist [sic] to greatly aid the naturalist in his researches, giving him in a few minutes drawings of invisible objects penciled by nature’s own hand, which it would be impossible for him to obtain in any other way.”

  John Whipple’s affirmation of the daguerreotype as a scientific tool was not exclusive to the microscopic realm. He certainly contemplated its potential in astronomy, for he tried to photograph the Moon by exposing sensitized plates for three to five seconds at the focus of a small telescope. The results were dismal, yet instructive. Under a magnifier (the images were a mere half-inch wide), he could make out the broadest aspects of the Moon. But because his telescope was stationary, the lunar forms were smeared out by Earth’s rotation.

  Whipple realized that a more promising instrument for celestial photography stood right across the Charles River in Cambridge: Harvard’s Great Refractor. Not only did the vaunted telescope have a far larger aperture—promising shorter exposure times—its clockwork drive was designed to track heavenly bodies, keeping them centered in the eyepiece as they marched across the night sky. With such an instrument, Whipple figured, he could take what was only barely discerned by the human eye and transform it into “a fixed fact for the naturalist to study at his leisure.”

  On the afternoon of October 23, 1847, William Bond opened up the observatory dome for John Whipple and rotated it until sunlight poured in. Perhaps distracted by conversation or by the evening’s public observing session, Bond swung the telescope unthinkingly toward the Sun. The focused beam shot out of the eyepiece and instantly burned a hole in his coat sleeve. It was only when he felt the intense heat on his skin that he snatched his arm away. Clearly, the Sun’s light was already sufficiently intense that it didn’t need the amplifying power of a fifteen-inch telescope. For safety’s sake, the two men decided to conduct their trial with a smaller telescope next door. Several attempts were made to capture a focused image of the Sun, but Bond’s diary entry says no more than “Mr. Whipple was satisfied that he should be able to accomplish the object.”

  According to the observatory’s annual report, Whipple and Bond made other attempts to image the Sun’s disk in 1848, all of them failures. Still, Bond asserts in his report that “we do not despair of ultimate success, when our time and means are adequate to the requisite expenditure.” In private, he was less sanguine. Bond’s allusion to adequate time might be an oblique reference to his exasperation with Whipple’s pursuit. Testing an untried technology, no matter how promising for the future of astronomy, was not Bond’s highest priority. The observatory’s stated mission was to conduct and report measurements of star and planet positions, and to use the telescope’s unique capabilities to carry out visual studies of planets and comets. Every time John Whipple showed up with his camera, the delicate micrometer used to measure celestial positions had to be removed from the rear end of the telescope. Putting it back afterward involved time-consuming readjustment and recalibration. Evidently, George Bond was more tolerant than his father to these periodic interruptions for photography. William Bond would have shunted Whipple to a smaller telescope, but George pressed for use of the Great Refractor. It is the younger Bond who would become the astronomical profession’s most vocal evangelist for celestial photography.

  On December 18, 1849, while the Bonds were making micrometer measurements of the position of Mars, Whipple and his partner William B. Jones arrived, this time to photograph the Moon, presently in its crescent phase. William Bond’s sigh of frustration is practically audible in a note he jotted afterward—the micrometer, he points out, had been secured to the telescope continuously for almost a year. Nevertheless, he removed the fragile measuring device. He makes no mention in his note of the outcome of the evening’s picture taking. Presumably, this effort was as unsuccessful as the solar attempt that preceded it.

  In an 1853 letter to the Photographic Art-Journal, John Whipple writes: “Nothing could be more interesting than [the Moon’s] appearance through that magnificent instrument: but to transfer it to the silver plate, to make something tangible of it, was quite a different thing.” In our age of point-and-shoot digital cameras, it’s difficult to imagine the challenges facing a nineteenth-century daguerreotypist. In the realm of early nature photography, the Moon was an obvious target. Big and bright to the eye, it nonetheless defied the best efforts of seasoned photographers, especially those who tried to capture a magnified lunar image through a telescope. The inevitable result wasn’t worth the trouble: a tiny, oblong, whitish splotch with no discernible features—like a dab of paint on a darkened slab.

  In a critical way, the eye is more forgiving than the camera of the hard realities of astronomical observation. The roiling of the atmosphere, the vibrations of footsteps on the observatory floor, the rumble of passing vehicles—all contribute to an incessant shaking of the telescope. Imperceptible to the bystander, these minute jostles are made manifest to the astronomer by the telescope’s essential function: to magnify things. Looking at a star in the eyepiece, one sees, not a languid speckle against the firmament, but a crazed firefly, darting about in random fits. Only occasionally does the star image hover at a central spot and is vividly seen. It is these rare moments of supreme clarity that visual astronomers prize: when a double star shows itself as a distinct pair of pinpoint lights instead of a single, elongated glow; when a lunar mountain peak settles into crisp definition, revealing its jagged shadow over the land; when a swirling storm on Jupiter rises out of its turbid cloak. For centuries, observers have coveted these brief, privileged aspects of the heavens. That’s one reason why they risk frostbite to study Saturn’s rings on a frigid February night or lug their telescope up a mountain to peer through one less layer of our restive atmosphere. And it’s one reason why visual astronomers were initially dismissive of the new photography. It conferred, as yet, no advantage over the human eye.

  A photographic plate is fundamentally different than the eye: it is endowed with a chemical-based memory for light—once a ray of light triggers the chemical reaction, a visible record of the event is imprinted on the plate. (A chemical fixing agent renders the image permanent.) This means that the nervous jitter of a bright star leaves its trace on the plate, building up a swollen blob of light many times larger than the true pinpoint image of the star. Thus, stars in the earliest photographs registered as bloated variants of themselves—if they registered at all. Likewise, extended objects like
the Moon or a planet appeared as fuzzy mirages, all but the grossest details washed away.

  Before releasing any astronomical photograph to the world, John Whipple and the Bonds knew that they had to capture an image that rendered detail comparable to that seen by a sharp-eyed observer peering through a telescope. The astronomical community would dismiss anything less. What factors made it so hard, in the 1840s infancy of the photographic art, for an expert like Whipple to take a decent daguerreotype of the Moon through a telescope?

  A daguerreotype plate is only marginally sensitive to light, requiring long exposures even in the glare of day. (Early portrait photographers located their studios on the top floor of buildings to gain access to skylights; nevertheless, an exposure of twenty-seconds duration was required.) Even a relatively bright celestial object like the Moon only grudgingly impresses itself on the plate’s chemical substrate. Concentrating the Moon’s light by means of a telescope helps, but a significant time exposure is still required to capture the image. Only with the advent of more sensitive photographic emulsions, starting in the 1850s, did “snapshot” lunar imaging begin.

  The execution of time-exposure photographs through a telescope is problematic. Every instant the camera shutter is open, the telescope is being whipped around at many hundreds of miles an hour by Earth’s rotation. Consequently, a celestial object centered in the telescope’s eyepiece creeps toward the edge of the viewing field until it disappears from sight. Most telescopes are equipped with a hand-crank mechanism that nudges them along and restores the straying object to its central place. Of course, the clocklike regularity of Earth’s spin lends itself to automated versions of this manual device. Whether an old fashioned, weight-driven gearbox or a modern, computer-controlled electric motor, the turn of the telescope can be set to match the rotation rate of our planet, only in the opposite direction. As a result, the telescope tracks celestial objects as they arc across the night sky. (Strictly speaking, this applies only to objects outside the solar system; the orbital movement of, say, the Moon or a planet causes it to go out of sync with the telescope’s clock drive.)

  No matter how excellent a telescope’s optics, the instrument’s photographic potential can be ruined by an inaccurate drive. A drive that is too slow or too fast stretches a pinpoint star image into a line on the photographic plate. Every lurch or stumble likewise leaves its imprint for posterity. Whipple struggled mightily to deal with the Harvard refractor’s so-called Munich drive, which was ill-matched to the stringent requirements of time-exposure daguerreotyping. He reported that the friction-based mechanism “had a tendency to move the instrument a little too fast, then to fall slightly behind. By closely noticing its motion, and by exposing my plates those few seconds that it exactly followed between the accelerated and retarded motion, I might obtain one or two perfect proofs in the trial of a dozen plates, other things being right.”

  Another factor that hindered the advancement of celestial photography was the difficulty in focusing the telescopic image onto the camera’s plate. Focusing is accomplished by shifting the eyepiece (or photographic plate) closer or farther from the telescope’s objective lens. The adjustment is exquisitely sensitive; a mere tweak of the eyepiece position substantially alters image clarity. Early cameras had a ground glass screen that rendered the image visible before the plate was inserted. Brilliant celestial bodies like the Sun or the Moon were visible on the screen, yet even the brightest stars barely showed up.

  Focusing was further complicated by the chemical nature of the daguerreotype plate. The human eye is most sensitive to midrange colors of the optical spectrum, such as yellow and green; by contrast, a daguerreotype plate is most sensitive to blue, violet, and ultraviolet light. This would not matter, except for an inherent property of refractor telescopes of the age, including Harvard’s: they were all designed for optimal performance using the human eye, not the camera.

  A simple objective lens focuses light of different colors to different distances behind the lens. Thus, the focal point for the red component of a star’s light falls at a different position along the telescope’s axis than the focal point for the blue component of the star’s light. (Light emanating from most celestial objects is a comingling of many colors.) No matter where the viewing eyepiece is placed, the magnified image is marred by colored fringes. This condition, known as chromatic aberration, is to a degree ameliorated by the use of a pair of nested lenses—a doublet—each made of a glass with a slightly different index of refraction. A common achromatic configuration is a convex (converging) lens of crown glass coupled with a concave (diverging) lens of denser flint glass; the convergence of various colors by the convex lens is partly offset by a divergence from the concave lens, such that the colors focus more tightly together. However, a doublet can merge the focal points of only a selected pair of colors; although colors adjacent to these remain somewhat dispersed along the axis, image fringes are significantly reduced.

  Because the human eye is most sensitive to midrange colors like yellow, nineteenth-century refractors were fitted with achromatic objectives that merged the focal points of colors flanking yellow, that is, red-orange and green. This arrangement reduces the dispersion of all three colors. But such an objective cannot simultaneously accommodate blue and violet rays, which are focused to a somewhat different position. In Harvard’s Great Refractor, whose focal length is around twenty-three feet, violet rays converge about an inch behind yellow rays. Placing a violet-sensitive daguerreotype plate at the telescope’s visual focus yields a compromised photograph. Only after the Harvard photographers positioned their plates an inch or so farther out, at the photographic focus, did they produce more vivid renderings of cosmic bodies. (Reflector telescopes, which use a mirror as the objective instead of a lens, do not suffer from chromatic aberration.)

  A more general criticism in John Whipple’s 1853 letter to the Photographic Art-Journal echoes the Bonds’ opinion about observing conditions in New England. Whipple writes of “the sea breeze, the hot and cold air commingling, although its effects were not visible to the eye; but when the moon was viewed through the telescope it had the same appearance as objects when seen through the heated air from a chimney, in a constant tremor, precluding the possibility of successful Daguerreotyping. This state of the atmosphere often continued week after week in a greater or less degree, so that an evening of perfect quiet was hailed with the greatest delight.” George Bond suggested that future generations of telescopes be placed in locations most advantageous to astronomy. In particular, he cited the dry, high desert regions of western South America. Today, this area is host to some of the largest telescopes in the world.

  On July 16, 1850, after Whipple had completed a series of daguerreotype experiments with Harvard’s small telescope, George Bond invited him to once more try the Moon with the large instrument. Again the micrometer was removed, this time interrupting nightly measurements of a comet’s path in the sky. The camera was secured in its place, without an intervening eyepiece, relying only on the converging power of the objective lens. Whipple’s images of the first-quarter Moon were poor. But later that night, Bond pointed the telescope toward brilliant Vega, in the constellation of Lyra, the second brightest star in the sky’s Northern Hemisphere. Whipple’s ninety-second exposure, aided by his skillful tending of the recalcitrant Munich drive, produced the first-ever daguerreotype of a star other than the Sun. A follow-up exposure of the double-star Castor revealed the pair as an elongated globule of light, the telescope’s jittery drive preventing their separation into distinct specks. Attempts to image fainter stars failed, regardless of the length of exposure.

  George Bond’s announcement of the stellar daguerreotype in the Boston Advertiser named Whipple as an assistant, although his expertise was surely essential to the night’s success. Bond marveled at how Vega’s rays had retained their power to stimulate a chemical reaction despite their long passage through space—a voyage that had begun some twenty years earlier, before Dagu
erre had developed the technology that now secured the starry portrait. Bond further pointed out what is obvious today, but unproven in his day: the light from the Sun and the stars must be fundamentally similar, for each activates the human retina and the photographic plate. The physical laws governing the production of light are presumably no different in the deep cosmos than in the solar system, a notion already accepted for Newtonian mechanics.

  Bond’s closing statement was a clear expression of where he thought celestial photography was heading in the long term: “It is our purpose to pursue the subject of daguerreotyping the stars, proceeding step by step from the brightest to those of lesser magnitude. We do not despair of obtaining ultimately, faithful pictures of clusters of stars and even nebulae.”

  Despite George Bond’s enthusiasm, Whipple and his colleague Jones did not return to Harvard for another eight months. On the evening of March 12, 1851, they took six daguerreotypes of the first-quarter Moon through the large telescope, although “much troubled by clouds and with an unsteady atmosphere.” To no one’s surprise, the pictures were blurry; the camera plate had been held at the telescope’s visual focus. Nevertheless, the results were sufficient to indicate an optimal exposure time of ten to fifteen seconds for the next attempt. On March 14, with the Moon swollen to a gibbous phase, a total of thirteen plates were exposed at various distances beyond the visual focus. Each advance toward the telescope’s photographic focus produced a more distinct image of the Moon. “The effect was at once apparent,” George Bond noted, “in the great improvement of the picture which is now obtained so as to give a better representation of the Lunar surface than any engraving of it, that I have ever seen.”

  Enlargements of the Harvard lunar daguerreotypes were an instant sensation at the 1851 Crystal Palace exhibition in London, acknowledged to far surpass any previous rendering of the Moon. The Annual of Scientific Discovery enthused, “We have rarely seen anything in the range of the daguerreotype art of so great beauty, delicacy, and perfectness, as the pictures referred to. The inequalities and striking peculiarities of the moon’s surface are brought out with such distinctness, that the various mountain ranges, highlands, and isolated peaks are at once recognized.”