4 Photology

Late Enlightenment Photochemistry and Black Skin

Modern photochemistry, launched in the 1770s by the Swedish chemist Carl Wilhelm Scheele and then mainstreamed by Jean Senebier, was a pan-European affair in which Black skin remained an ever-present reference.1 In 1795, James Watt, Thomas Wedgwood, and Thomas Beddoes made plans to create the Pneumatic Institution, a clinic treating patients with ailments ranging from consumption and breast cancer to depression, using various combinations of gases.2 It opened in 1798 in Bristol, England’s principal port for the transatlantic slave trade, and ran for a short time. It employed a young chemist, Humphry Davy, who had just developed a laughing gas. The institute’s director was Beddoes, who had received an MD from Oxford and would have been named professor of chemistry there but for his penchant for the French Revolution and the new chemistry of Antoine Lavoisier—both perceived as anti-British. Beddoes lectured against slavery and collaborated with Samuel Taylor Coleridge’s abolitionist newspaper in the early 1790s.3 It was Beddoes who introduced Coleridge to German Idealism, and to Wedgwood as well.4

Beddoes was well versed in photochemistry. In 1786, he translated a book of Scheele’s experiments referencing light-sensitive silver compounds.5 In 1796 he reviewed An Essay on Combustion with a View to a New Art of Dying and Painting by chemist Elizabeth Fulhame for The Monthly Review (Stansfield, Thomas Beddoes, 109). Fulhame presented catalytic methods for depositing metals on cloth and paper, including “small films of reduced silver” made from silver nitrate. She references Scheele’s photochemical experiments from another English translation directed by Joseph Priestley.6 As a medical doctor, chemist, and German translator, Beddoes oversaw experimental therapeutic applications at the Pneumatic Institution. Early in his career, Beddoes treated a free Black man who came to him. “At Oxford in 1790,” he writes, “I had proposed to a distressed negro, to try to whiten part of his skin with oxygenated marine acid air [hydrochloric acid]. He was to exhibit the appearance, if it should be curious, for the relief of his family.” The Black patient had “ulcerations” between his fingers, and the treatment caused him “severe pain.” Beddoes concludes: “The back of his fingers had acquired an appearance as if white lead paint had been laid upon them, but this did not prove permanent.”7 It is unclear what “relief” was sought from exactly what distress; Beddoes’s veiled words do hint at a young man suffering from internalized racism.8 As Beddoes had flayed and blistered his own fingers to observe the action of various gases, his aggressive treatment was not unusual.

Well publicized in medical literature, the attempted cure was notoriously taken as further evidence that “the black colour of negroes depends upon a black pigment, situated in this substance [rete mucosum],” not found in white skin.9 Beddoes also used silver nitrate medicinally, treating a white child’s hand to cure excessive perspiration—an equally painful treatment.10 Among books Beddoes reviewed for The Monthly Review was Medicine Informed by the Physical Sciences (1791) by French chemist Antoine-François Fourcroy (Stansfield, Thomas Beddoes, 256). Fourcroy mentions the case of a priest near Hamburg, Germany, who absorbed “nitric silver dissolution” for a liver ailment and whose skin became “almost entirely black.” Silver nitrate remained a widely used topical ointment through the nineteenth century for hair ailments, acne, impetigo, cauterization, color whitening, and tattoo removal, and even conditions like epilepsy.11 An authority on skin diseases indicates in the 1820s that silver nitrate produces “a tanned hue of the skin analogous to that of mulattoes,” adding that a patient he treated with silver nitrate was “usually taken at first to be a mulatto.”12

Skin color anomalies were of particular interest for natural philosophers like Pierre-Louis Moreau de Maupertuis and Georges-Louis Leclerc, count de Buffon, and in the 1790s unexplained color mutations were sensationalized as both medical puzzles and public exhibitions; this signaled their heightened stakes for the racialized order.13 In 1795, London MD William Charles Wells, whose research focused on physiological optics, examined a white woman who displayed patches of very dark skin from birth.14 Wells acknowledges monogenism, by then widely accepted: “Blackness of the skin in negroes is no proof of their forming a different species of men from the white race” (Wells, “Account of a Female,” 431). After warning that the supposed “deformity of [Black peoples’] features” is only due to “our [e.g., white people’s] notions of beauty,” he adds: “Their present appearance may possibly be regarded not only as a sign, but as a cause of their degraded condition, by preventing, in some unknown way, the proper development of their mental faculties; for the African negroes have in all ages been slaves” (438, 439). While Wells echoes the victim-blaming of Johann Kaspar Lavater, he shifts anti-Blackness from skin and features to mental and civilizational underdevelopment—the hallmark of nineteenth-century scientific racism.15

Interestingly, Wells indicates that “Sir Everard Home,” who examined the woman with him, opined with clear prejudice that “the dark arm smelt more strongly than the white,” which Wells did not confirm (Wells, “Account of a Female,” 429, 430). Wells further conjectures “from observations lately made on two negroes, that the action of the sun tends rather to diminish than augment the colour of their race” (431). As “both of those persons were born in European settlements,” it is possible that the two Black men on whom Home experimented two years later (see introduction) were the same individuals (431).

What seems clear from all these cases is that new photochemical studies of silver nitrate in the 1790s piggybacked on its former dermatological applications to redirect the etiology of Black skin. Edward Bancroft, the author of an influential reference work on color-making, stated in 1794 that “silver nitrate also gives the skin a black colour, which cannot be effaced, but by a removal or change of the skin itself.” He adds: “The blackness of the negro child is found, by observation, to be considerably hastened by early exposure to strong light, which seems to favor the absorption, or combination of oxygene; an effect which is not surprising, since, by many of Mr. Sennebier’s experiments, the light was found to act in this way through coverings of greater thickness than those which oppose its access to the reticular membrane in negroes.”16 This new photological thesis of Black skin cut both ways. On the one hand, it depathologized Blackness through an established and superficial natural phenomenon. On the other hand, it added an unseeable physiological difference potentially related to “the development of mental faculties.” However, these supposedly scientific debates were overdetermined by the context of 1760s Caribbean rebellions by enslaved peoples, especially the 1791 Haitian Revolution, which had unprecedented repercussions on black-and-white racial rhetoric and the philosophy of history.17 Let us note that this black-and-white approach to skin color forestalled other approaches, such as Thomas Clarkson’s gradation model and Martin Delany’s prescient 1850s theory of quantitative pigmentation.18

Black-Making Rays

Determinant for this study was locating William Herschel’s notes on “black-making rays” in the Royal Greenwich Observatory Archives. To my knowledge, these mysterious rays have never been commented on. Their story begins in 1800 when William Herschel discovered infrared or “calorific rays” after experiencing a warm sensation around his eyes when looking at red-colored stars in the eyepiece of his telescope. The relationship between heat and light stood at the center of physics and chemistry in the last two decades of the eighteenth century, and the only published research of Thomas Wedgwood was in that critical area.19 Herschel placed thermometers in a camera obscura under a light beam reflected from a solar microscope and refracted through a prism. He found that the hottest area laid outside the visible spectrum beyond red, confirming that optical rays were the cause since they reflected and refracted like visible light. In 1801, Johann Wilhelm Ritter, a polymath from the Jena circle around Friedrich Wilhelm Joseph von Schelling, Johann Wolfgang von Goethe, and Scheele, conjectured that another variety of “invisible rays” lay at the other end of the spectrum—given the Jena circle’s shared belief in the polarity of natural forces. Exposing paper imbued with silver chloride to the area past the blue end of the spectrum, he found that it darkened faster than in the most reactive area of blue established by Senebier.20

After his own discovery, Herschel sought a new theory of light. His idea was based on “modifications of light”—how light’s trajectory alters at the contact of matter. For white light, he wrote, the signature deviation is reflection on a mirrored surface, while for decomposed color rays it is refraction through glass. The question Herschel pondered was what ray corresponded to flexion—that is, the bending of rays at the edge of objects:

When light passes by an opaque body at a certain distance it is bent from its rectilinear course towards the body. This modification of light is well known and has generally been denoted very properly by the name of inflection.

This has been proved by different authors but most of the experiments they have given are fallacious. The unexceptionable one is that an opaque globe when exposed to the unconfined rays of the sun, the solar penumbra being properly allowed for, will cast a shadow which is less than it would have been if light had not been inflected toward the body*

*See the experiments of M. Marat published in 1780 and those of G. W. I in 1799.21

This important passage deserves a careful gloss, starting with Herschel’s surprising reference to Jean-Paul Marat. Elsewhere in his notes, Herschel confirms that “a work called Découvertes sur la lumière par M. Marat, contains likewise several experiments which, had they been properly understood by the author, would have laid open very different views to him from those he believed to see in them” (“Modifications of Light,” folio 14).22 Before turning to politics, Marat had been a physics experimenter and lecturer competing with Charles, with whom he had a run-in in 1783.23 Born in Geneva, Marat moved to Bordeaux as a teen to tutor the children of Pierre-Paul Nairac, a trader of enslaved people.24 In his twenties he moved to England, obtaining an MD from the University of St Andrews before returning to France as doctor to the guard of future King Charles X. Despite having no training in mathematics, Marat acquired a strong reputation as an experimenter in natural philosophy.25

In Physical Research on Fire (1780), Marat claimed to have discovered the underlying substance of heat, which he called the “igneous fluid,” immodestly comparing his discovery to that of electricity and Isaac Newton’s theory of light.26 His claim rests on a visual phenomenon he carefully observed: convection wisps of air rising from heated objects. To visualize them properly, he employed a solar microscope in a camera obscura (a “helioscope”) to silhouette objects placed on rollers against a movable screen and locate “the place where the image appears most distinctly” (Marat, Recherches physiques, 196–97).27 His book is illustrated with fine drawings by “Mad^me Ponce,” the engraver Marguerite Hémery Ponce who worked for the Comte d’Artois, Marat’s employer.28 These drawings feature silhouettes of airflow arabesques—combining silhouetting and hieroglyphs—which Marat interprets as imaging the yet unseen fluid of heat. He declared that a flame starts only when its “shadow has entirely crossed” the “bright band [raie lumineuse]” of igneous fluid surrounding it (27). He believed he had solved the enigma of combustion through the diffraction of rays: “Light rays constantly bend at the circumference of all bodies whose sphere of attraction they traverse,” he stated (196). In a complementary monograph also from 1780 titled Discoveries by M. Marat on Light, he examined more closely that “bright band [raie lumineuse].”29 Projecting light beams at blades and small holes in his camera obscura setup, he observed that the light band appeared within the shadow area, concluding that these “rays . . . are thus mainly attracted by the edges” (3). With an even smaller hole, “you will see the shadow of the [hole’s] edge surrounded with a bright aureole outside, darker midway, dark inside, and ever darker as it nears [the center] of the shaded area” (3–4). The result was confounding. It was as if light exchanged places with darkness when passing through the hole.

Newton thought that light rays deflect away from bodies. But the innovative rack focus in Marat’s setup enabled him to observe that the opposite was true: Light is attracted by matter. In an inspired experiment, Marat showed that rays bending around a small sphere converge into a small “luminous point” at the center of its shadow cone (Découvertes, 3–4, 7fn1, 10). Forty-two years later, this experiment, known as the Poisson Spot, was reproduced by François Arago and Augustin-Jean Fresnel, providing decisive proof that light is a wave. As Herschel noted, however, many of Marat’s experiments were hasty and shoddy, leading him to false and vainglorious claims. Marat concluded, for instance, that the igneous fluid invalidated gravitation and that Newtonian optics was wholly counterfactual. The subtitle of his book on light, Resulting from a Series of New Experiments Made Numerous Times Under the Eyes of Commissioners from the Academy of Sciences, was a plain exaggeration. The commission’s head examiner—Marie-Jean-Antoine-Nicolas de Caritat, marquis de Condorcet—required inclusion in the monograph of a warning that Marat’s experiments “do not seem to prove what the author imagines he has established” (iv).

Separating the wheat from the chaff, Herschel confirmed experimentally that light does bend toward matter (although he oddly mistakenly stated that Newton thought so too). His hunch was that invisible rays—infrared and perhaps ultraviolet—represented a new kind of light ray whose proper motion was deflection:

The novelty of black-making rays . . . will induce us to pause before we admit them; but has not each modification its particular properties? Reflection will not separate red-making from green-making rays, but refraction will do this. Neither reflection nor refraction, it might be said, will separate black-making rays from others whereas it seems that deflection will bring on their separation.

On the present occasion I must remark that this is not the first instance I have had of the appearance of black-making rays; and though hitherto I have always endeavored to evade such ideas as deceptions, I might for the future be less scrupulous. (Herschel, “Modifications of Light,” 10–11)

Herschel stayed publicly mum about his black-making rays theory for one simple reason: At the height of the Napoleonic Wars, British jingoism was so intense that any invocation of recent French science—a fortiori the work of Newton-denier Marat—was anathema. As we will see, Thomas Young was forced to cease research on the wave theory of light in 1804 for the same reason. The story of black-making rays does not end there, however. We return to it later in this chapter since in 1839 it occasioned a letter from John Herschel to François Arago in the context of the emergence of photography.

Black Light

Invisible rays and their linkage to both heat and photochemistry made the nature of light central to physics circa 1800, against the backdrop of the oxygen/phlogiston controversy.30 In quick succession, two other forms of blackness-in-light were found. William Hyde Wollaston, an MD and chemist studying light refraction, published a paper in 1802 stating that a “very narrow pencil of light . . . admitted into a dark room,” after decomposing through a prism into the color spectrum, showed “other distinct dark lines . . . that might be mistaken for the boundary of these colors.” These black lines (absorption lines) had never been noticed before. In a footnote, he adds that he also detected “invisible rays” beyond violet—independently of Ritter and using silver chloride as well—finding “that the blackness extended not only through the space occupied by the violet, but to an equal degree, and to about an equal distance, beyond the visible spectrum.”31

In the same 1802 issue of the Philosophical Transactions of the Royal Society, Thomas Young published “On the Theory of Light and Colours,” a momentous paper solving at once two enormous problems by linking them. Young was a prodigy who learned a dozen languages and digested Newton’s Principia and Opticks by age seventeen. At fourteen, he had resolved to “abstaining from the produce of the labor of slaves,” and the banker David Barclay later paid for the manumission of thirty enslaved persons at the urging of Young, who tutored his son.32 He was elected to the Royal Society at twenty-one after publishing a paper proposing that the eye lens is a muscle. In 1794, he had a meeting with the Herschels at their observatory in Slough, England.33 In 1796, after defending his MD thesis on the forty-seven sounds the human mouth can articulate, he traveled to Germany. On the way, he stumbled on two Englishmen on their grand European tour: Thomas Wedgwood and John Leslie, a specialist of heat science. In Weimar, Germany, Johann Gottfried von Herder eagerly awaited his arrival to discuss universal phonetics (Robinson, Last Man, 52). Fascinated by the hieroglyphic patterns of sound and light, and a key actor in the decipherment of Egyptian hieroglyphs, Young bridged the spirit of German Naturphilosophie and modern physics.

“On the Theory of Light and Colours” suggests that the eye has three distinct receptor cells for yellow, red, and blue, with other colors resulting from mixing. The larger proposal on which he had been at work is that light is a wave. With music as analogy, he both outlined the mathematical grounding for the WTL and chose the right frame for visualizing unseeable light waves: interferences.34 Before Young, it was thought that two soundwaves with different ratios (frequencies) remained separate in a musical chord. Young argued instead that they must combine, since the same particles of air can hardly vibrate at two frequencies at once. He extrapolated that the same occurred in light and proposed three ways for visualizing interferences. The first was a ripple tank, a water container with a transparent bottom illuminated from below and projecting ripple patterns on a 45-degree mirror. It showed that water waves combine their crests and hollows, and the same should be expected of light waves. Water wave interferences were known in Europe since 1678 but had been understood long before by Vietnamese fishermen who connected complex estuary tide patterns to the lunar cycle.35 Using that precedent, Young conceptualized his second visualizing method: the famous two-slit experiment splitting a light beam into two in a camera obscura and projecting the image of their interferences on a screen. In 1803, to verify that the phenomenon was not an optical illusion, he devised a third method: replacing the screen with “a strip of paper dipped in a solution of nitrate of silver,” on which “portions of three dark rings” were imprinted. While Charles, Wedgwood, and Henry Peter Brougham all produced fugitive photochemical images, they did not describe a single one in detail. Young’s print is thus the first photochemical image ever described.36

In his 1801 paper, Young spelled out the larger philosophical consequence of crests and hollows of light waves overlapping. In “Corollary IV. Of Blackness,” he stated that any “substance can become positively black” at the places where waves cancel each other when interference patterns are projected on it.37 This corollary expresses a radical idea that I believe is connected to Young’s antiracist stance: Blackness can result from light added to light. The word positively is key since it undoes the century-old preconception that both chromatic blackness and racial Blackness are a lack, a negative—the sheer absence of light or whiteness.

Recontextualizing Thomas Wedgwood’s Photochemical Dabbling

To sum up this chapter until now, in the wake of William Herschel’s discovery of invisible “caloric rays,” British physical optics led by Wollaston and Young evidenced three new kinds of species of black light: absorption lines (1801), ultraviolet (1801), and interferences fringes (1802). The last two were ascertained by photochemical blackening. This is the proper frame within which to reconsider the purportedly original source of photography: Humphry Davy’s famous 1802 article.

The title is worth citing in full: “An Account of a Method of Copying Paintings Upon Glass, and of Making Profiles, by the Agency of Light Upon Nitrate of Silver. Invented by T. Wedgwood, Esq. With Observations by Humphry Davy.”38 What jumps out immediately is a split in both subject matter and authorship: art reprographics and silhouetting; Wedgwood and Davy. A third author should be invoked, Young, since he was the journal’s physics editor and had a hand in its final version. Indeed, when the article appeared in June 1802, Davy was involved in replicating experiments on infrared and ultraviolet rays that Young had commissioned and that likely used silver nitrate imaging.39 There is no question that of the two authors of the paper, Wedgwood is the least knowledgeable about photochemistry. Davy’s terse account of Wedgwood’s experiments describes a simple transfer and stencil process. Paintings on glass and “the woody fibers of leaves, and the wings of insects” were placed on leather or paper treated with silver nitrate and illuminated, producing what Davy terms “profiles,” “outlines,” and “shades” (“Account of a Method,” 169, 167, 168). Davy indicates that using “a camera obscura” was “the first object of Mr. Wedgwood,” after “a friend” (169) told him about silver nitrate, but the images Wedgwood produced proved too faint to register (169).

Davy then describes his own experiments using “a solar microscope” in a camera obscura on “small objects” to make images on “prepared paper” held at “a small distance from the lens” (“Account of a Method,” 169). Like other experienced photologists, Davy makes full use of Senebier’s setup, most notably a convex lens. Davy compares the effects of silver chloride and silver nitrate, the first acting faster but insoluble in water, the latter acting more slowly and being soluble. He hopes that a means might be found for “destroying the compound,” thus “preventing the unshaded parts of the delineation from being coloured by exposure,” thereby fixing the image (170). Importantly, this last suggestion is not attributed to Wedgwood. Since the paper is couched as a tribute to his dabbling (and now ill) friend, if Wedgwood had used a lens, different compounds, or entertained the possibility of fixation, Davy would have certainly credited him.

Photography historians have conjectured about the identity of the unnamed “friend,” and there is a plethora of possibilities. Young, Wollaston, and Davy are the obvious first choices. But he could be any of the associates and assistants in the workshop of Josiah Wedgwood who were knowledgeable in photochemistry: William Bentley, James Keir, William Lewis, and head of research Alexander Chisholm. Older members of the Lunar Society funded by Wedgwood’s father represent a third avenue: Erasmus Darwin, Leslie, Priestley, Watt, and Beddoes. Any of them was more familiar with photochemistry than Thomas Wedgwood.40 A notorious letter from Watt to Josiah Wedgwood mentions “silver pictures,” which the latter had sent the former, and it has been wrongly taken as evidence for Thomas Wedgwood’s photoimaging.41 Yet all the actors above knew better than to confuse whitish-gray silver salt compounds with “silver” proper. The Wedgwood factory was experimenting at the time with silver plating, as Alan Barnes shows, so Watt’s “silver pictures” were almost certainly silver-plating samples.42 My overall point is not to diminish Thomas Wedgwood’s contributions but rather to contextualize them within collective photochemical imaging experiments in the early 1800s spearheaded by Wollaston, Young, and Davy as part of innovative investigations in physical optics.

Wedgwood’s family circle was very much interested in both hieroglyphic imaging and the camera obscura. After reading about Priestley’s work in chemistry and optics, Josiah Wedgwood Sr. wrote the following to his partner Bentley in 1779 regarding the education of his two sons: “If visible images could be made of these bodies, their unions, & changes, it would make the study pleasanter to them, & the painted images could be easier stored up in their memory & perhaps with more precision than the ideas alone without the assistance of such painted images.”43

In 1786, Robert Waring Darwin published an essay on “ocular spectra” that investigated negative afterimages and “retinal persistence.”44 The bulk of his research is thought to have been coauthored by his father Erasmus Darwin (Thomas Wedgwood’s uncle-in-law), who was convinced that optical images directly shaped mental images and ideas. Introducing his 1795 summa of natural philosophy, Erasmus Darwin figures his book itself as a camera obscura, writing: “Gentle Reader! / LO, here a CAMERA OBSCURA is presented to thy view, in which are lights and shades dancing on a whited canvas, and magnified into apparent life!”45 In the circle dominated by Erasmus Darwin, artificial image-making was discussed together with optical processes underlying perception, imagination, and cognition. When Beddoes argued in 1794 against Darwin’s thesis that the genesis of mental images begins with ocular spectra, Thomas Wedgwood took the side of his uncle (Barnes, “Negative and Positive Images,” 246–47). As both Barnes and Francis Doherty document, Thomas Wedgwood debated models of vision, perception, and imagination with his close friend Coleridge, who sided with Beddoes (Barnes, “Negative and Positive Images”).46 Thomas Wedgwood proponed a mechanistic model of experience centered on vision where serial perceptual images continuously imprint the mind. Coleridge opted for a model of perceptual experiences reinterpreted by revisualization and re-creation—that is, poetic in the original sense of image-making (poieîn). For Thomas Wedgwood, by contrast, visual perception was a self-registering apparatus (Doherty, “Tom Wedgwood,” 309). Direct impressions, for Wedgwood, are complemented by extrapolated visualization: “The idea of the invisible part of the globe instantaneously blends with the perception of that which is visible, and they jointly form my notion of the globe. . . . Thus a standard visual idea of every object is formed, which instantly blends with every fugitive perception, and corrects it.”47 Thomas Wedgwood inquired about retinal impressions in a letter, mentioning “his own attempts at drawing the different positions of the wings of birds in flight, which would ‘coalesce’ into the impression of smooth movement,” in Barnes’s words (“Negative and Positive Images,” 255). For his brother Josiah Wedgwood Jr. writing in 1800, Thomas Wedgwood’s general philosophical agenda in the years when he dabbled in photochemical experiments was “no less than Time, Space, and Motion” (cited in Litchfield, Tom Wedgwood, 207). This befits a protocinematographic approach to vision rather more than a pre-photographic one, as Matthew C. Hunter keenly proposes.48

An opium user, Coleridge favored the creative genesis of visual impressions, “the rising up of Spectra in the eye,” as he puts it in a letter.49 Inspired by his readings of German Idealism, he made imagination the central faculty as he insisted to Thomas Wedgwood in 1803: “William Hazlitt is a thinking, observant, original man, of great power as a Painter of Character-Portraits, and far more in the manner of the old Painters than any living Artist, but the objects must be before him; he has no imaginative memory.”50 When he fashioned his influential poetics a dozen years later in Biographia Literaria, Coleridge drew an even sharper contrast between simple mimesis and creative imagination. The former, which he calls “fancy,” is “a sort of mental camera obscura manufactured at the printing office, which pro tempore fixes, reflects, and transmits the moving phantasms of one man’s delirium.” Pure imagination, by contrast, “is creation rather than painting, or if painting, yet such, and with such co-presence of the whole picture flashed at once upon the eye, as the sun paints in a camera obscura.”51 Coleridge rejects the kind of animated visualization proponed by Erasmus Darwin and Thomas Wedgwood in favor of a “flash” poetics closer to a photographic snapshot. Interestingly, the camera obscura appears on both sides of Coleridge’s models of imaging, suggesting a wider conceptual currency of photocinema formations by around 1815.

French Physical Optics: From the Wave Theory of Light to Pre-Photography

The remarkable research in physical optics and the WTL produced in England ended with a whimper with the short-lived Treaty of Amiens between France and England in 1802–1803. In October 1801, during treaty negotiations, Napoleon Bonaparte obtained approval from England to send an expeditionary force of over twenty thousand troops to recapture Saint-Domingue from formerly enslaved fighters led by Toussaint Louverture.52 In 1802, as England returned Martinique, Tobago, and Saint Lucia to France, Napoleon passed a secret law confirming that “slavery will be maintained” and “the trade of blacks and their importation in the above-mentioned colonies, will take place according to laws and regulations prior to 1789.”53 Decrees restricting entry to France of Black people and other people of color (1802) and forbidding marriage on French soil between Black people and white people (1803) were passed as well.54

As Napoleon crowned himself emperor (1804), the two pro-Napoleonian leaders of French science, astronomer Pierre-Simon, marquis de Laplace and chemist Claude-Louis Berthollet, dictated a strict agenda centered on mechanics, light corpuscles, and celestial bodies. Laplace headed physical sciences due to the prestige of his Exposition of the System of the World (1796), the first secular cosmology based on a similar nebular hypothesis as Immanuel Kant’s and William Herschel’s.55 French scientific research at the beginning of the nineteenth century reflected a combined allegiance to Napoleonic rule, universal reason, and expansionist foreign policy. Within this agenda, optics was strongly promoted as a theoretical litmus test for the unification of physics and mathematics into a universal corpuscular theory. But there was a very pragmatic reason as well: the continental blockade. Cut off from its colonies and from England’s leading industries, Napoleonic France had to boost very quickly all areas of fundamental and applied research, starting with lens-grade production without England’s superior and proprietary crown-glass.56

In 1806, Laplace tasked mathematician and astronomer Jean-Baptiste Biot with investigating the refraction of light in gases. Biot was aided by a young astronomer, François Arago.57 After attending École Polytechnique for two years, Arago was named secretary astronomer at the Paris Observatory in 1805—even though in 1804 he had led a protest at the school against Napoleon, whom he detested.58 In 1806, Arago published a paper on the speed of light before being sent to Spain in 1807 to finish the geodesic survey of the meridian from which the meter was to be computed.59 When Napoleon invaded Spain in 1808, Arago became, de facto, a spy. He underwent a year of perilous captures and spectacular escapes from Spain to Morocco and Algeria before returning to Paris in 1809. Reincarnating the Maupertuis-like figure of the astronomer turned adventurer, Arago became an overnight sensation. Over the next decade, he progressively overtook Laplace as the leader of French physics, not through brilliant theories or major discoveries but because he was a keen experimenter and teamwork leader with an encyclopedic knowledge of astronomy, optics, electromagnetism, and meteorology. Unlike his older colleagues, he was an anglophile who strongly favored transnational collaboration, notably with Young, John Herschel, Adolphe Quetelet, and Alexander von Humboldt. A proponent of free speech and free education who admired England’s constitutional monarchy, he embraced republicanism in the 1830s. Elected to Parliament, he pushed unsuccessfully for so-called universal suffrage (albeit limited then to male property-owners), became an opponent of the July Monarchy, and was a leader of the revolutions of 1848, during which he oversaw the abolition of slavery in French colonies (see chapter 5).

When Arago was named secretary of the Académie des Sciences in 1830, it signaled that the central wager of his scientific career—that the wave model of light has a better explanatory power than corpuscular and emissive theories—was won. Knowing Young’s work closely, he adopted the WTL around 1810 and systematically recruited junior researchers who could assist in its proof, notably a transportation engineer named Augustin-Jean Fresnel.60 Prior to joining Arago in 1814, Fresnel had submitted a soda-making process to the committee on new innovations in 1811. Commissioners Louis-Jacques Thenard and Joseph-Louis Gay-Lussac forwarded it to the arbiter in chemistry at the Académie des Sciences, Nicolas-Louis Vauquelin, who never read it. Fresnel was only told that his process was not economical. Disappointed, he pored over scientific journals, stumbled upon debates about the nature of light, and retooled his career. This minor episode is worth mentioning because in spring 1811, the Niépce brothers followed the exact same path. They devised an indigo ersatz process to compensate for the loss of Saint-Domingue’s production. Thenard and Gay-Lussac reviewed the process, turning it down on similar uneconomical grounds in 1813.61 Looking for another area of innovation, they turned to the print and reprographic sector and then to pre-photography.62 In other words, the WTL and Niépce’s heliography got their respective contingent start from the same industrial context: the French metropole bereft of its stolen Caribbean labor.

In 1814, Arago tasked Fresnel with researching the deviation of light rays at the periphery of objects—the very phenomenon studied by Marat and William Herschel that led Young to focus on light interferences. With a solar microscope projecting a light ray through a camera obscura onto thin wires, Fresnel noted in 1815: “Since intercepting the light from one side of the wire makes the internal fringes disappear, the concurrence of the rays that arrive from both sides is therefore necessary to produce them.” Fresnel, who could not consult Young’s work for lack of English (unlike Arago), rediscovered interference fringes (Buchwald, Rise of the Wave Theory of Light, 117–19). His 1816 memoir reexplaining diffraction phenomena concludes that they “confirm the system that considers light as vibrations of a particular fluid.”63 The emissionist camp headed by Biot and Laplace set up a prize to adjudicate “the nature of these motions” taking place in “the diffracted bands that form and propagate outside the shadow of bodies” as well as “within the shadow proper”—again, the very terms used by Marat and William Herschel (170). After Fresnel received the prize in 1819, Siméon-Denis Poisson, an emissionist, worked out a damning mathematical objection from Fresnel’s own theory: If light was projected at an opaque disk of a certain size, according to Fresnel’s equations a white spot should appear smack in the middle of its umbra. Since that was palpably absurd, so was the theory. An experiment was ceremonially set up with Poisson, Biot, Arago, Fresnel, and others present, and a white spot indeed became visible in the middle of the shadow as predicted. This was what Marat had described in 1780 and what, in part, led William Herschel to search for black-making rays.

The testing apparatus for that experiment was constructed by Arago himself, as Fresnel indicates in “On Light” (1821), a key document bridging the WTL and pre-photography.64 When Fresnel began his darkroom experiments in 1815, it was also Arago who had suggested the use of a solar microscope (Fresnel, “Mémoire sur la diffraction de la lumière,” 236). To eliminate uncertainty regarding the effect of light’s diffraction at the edges of bodies, Fresnel had developed the so-called double-mirror experiment in early 1816, a spin-off of Young’s double-slit experiment—again at the urging of Arago. In that experiment, a ray of light was bounced onto two adjacent mirrors at a slight angle to make their reflections interfere (Buchwald, Rise of the Wave Theory of Light, 137). In 1821, Fresnel used a heliostat to still the sunbeam and measure the distance between fringes, verifying that starlight produces fringes as well. He pointed out that light as “a certain mode of vibration of a universal fluid” exerts a chemical action that should be regarded less as a combination of “molecules” than as the rearrangement of the structure of matter—a continuation of Senebier’s insight (Fresnel, “De La Lumière,” 10, 116, 135).

A postscriptum hastily inserted at the end of the volume containing “On Light” is crucial for pre-photography. It was added because Fresnel became belatedly aware of an experiment Arago had conducted: “By projecting on freshly prepared silver chloride the fringes produced by the interference of two pencils of light reflected from two mirrors at a slight angle between them, Mr. Arago has noticed that [the fringes] traced black lines equally spaced and separated by white intervals.”65 Depending on the placement of the photosensitive paper within the area of interference, the “same rays” would blacken the silver chloride at certain distances but not others, providing material proof that the waves added up or canceled each other. Fresnel specifies that a heliostat must be used to counter the Sun’s motion, that the exposure should be at least ten minutes, and that a semicylindrical lens should be used as Arago suggested (Fresnel, “Post-Scriptum,” 537–39). This camera obscura “apparatus [appareil]” that combined a specified lens, a silver chloride covered “plate,” and a precise exposure time produced a series of photochemical prints that imaged and visualized a 3D field of light interferences. It was a great deal more sophisticated than the setups with which Niépce was dabbling at the time. Arago’s photoimages showed a series of parallel black striations in a narrow band in the middle of the white plate, with some prints showing less striation when the plate was closer or farther from the mirrors. The iterative process between photochemical prints, modifications of the setup, then new prints improving the sharpness of the bands places Arago’s experiments among similar trial-and-error practices as experiments by Niépce, Daguerre, and Talbot. As for the absence of fixation, the reason is simple: The prints do not matter, only the description of how they can be replicated. Fresnel’s detailed instructions indeed aim to enable the exact reproduction of the experimental setup rather than the exact reproduction of what it images.

Dated August 1821, these experiments have not been sufficiently recognized in the accepted prehistory of photography.66 Yet John Herschel knew they belonged to it. In the unpublished 1839 version of his famous essay on photography of 1840, he stated unambiguously that such photoimages “by Mssrs. Arago and Fresnel” did pioneer “a strictly photographic process.”67

By 1839, John Herschel and François Arago were recognized as the leading authorities in photology and they respected each other’s commitment to open and internationalized science. This is why, in summer 1839, the former disclosed to the latter his father’s quixotic black-making ray experiments, which I alluded to earlier, as Arago was involved in writing a biographical sketch of William Herschel and had queried his son. This candid and unpublished letter (which I located in the archives of the Paris Observatory) is significant for three reasons. First, John Herschel confirms that William Herschel actively pursued black-making rays. Second, it is dated July 1839, when England was in a diplomatic rift with France for its support of Muḥammad ʿAlī of Egypt. And third, at that very time, Talbot, whom John Herschel had assisted, was publicly challenging Daguerre, whom Arago had championed, over the invention of photography—a word John Herschel had just coined.

Dated “Slough, July 1–5, 1839,” it reads:

The analysis of the solar rays was always a very favorite object of [William Herschel’s] pursuit, and his detection of the calorific rays beyond the visible spectrum is well known to every photologist. But there was another branch of photology which led him into many and laborious experiments. . . . The shadows of objects in clear sunshine are marked, according to his observations (which my body may verify) by two phenomena—1st a bright edge or border, wholly without the shadow, more strongly illuminated than the space far exterior to it—and 2nd, a band or fringe within the shadow, darker than the shadow itself. I speak of shadows not as seen in darkened chambers and as cast by objects of small dimensions—but in the open sunshine and from large objects. Of these phenomena the theory of diffraction renders a satisfactory account. But that theory was unknown to him, and the phenomena, being studied under the circumstances above mentioned could never have sufficed for the formation of a distinct theory. I consider it therefore not a little remarkable that these phenomena, so studied, should have led him to a conclusion he considered too strange and too bold to publish. Viz.: that there are in the solar rays some which have the reverse property to illuminating & to which he used to give the name of black-making rays! To such rays, inflected into the shadows according to Newton’s theory of inflection (of which he was always an advocate) he ascribed the blackest at the inner edge of the shadow—and to their absence, the bright fringe exterior to it. This power of illumination and obscuration which he thus attributed as inherent qualities to rays of different species we now, in the theory of interferences admit, as properties of the positive and negative phases of the undulations constituting one and the same ray. I beg you to observe that it is now for the first time that I make mention of this curious point in my father’s scientific history, and that, if the nature of the work you are engaged in, leads you into any account of his scientific or rather intellectual character you are at liberty to mention it, on my authority. I would not trust the mention of it to any one else than you, however.68

This letter attests to John Herschel’s unease at the possible revelation of William Herschel’s black-making rays conjecture, fearing it might tarnish his scientific reputation. Yet he trusts Arago—and Arago alone—to make the call. More broadly, the letter demonstrates the conceptual contiguity between photology, interference phenomena and the WTL, black-and-white rhetoric—“positive and negative phases of the undulations”—and photography.

French Photochemical Research, 1802–1820

Photography historians have not queried whether and how photochemical experiments by Thomas Wedgwood, Davy, and Young disseminated to France. A cursory foray into the archives shows that they were quickly and profusely reported on in the French scientific press. Berthollet reported on Wedgwood’s experiments as soon as they were published in 1802, and in an 1803 textbook on chemistry he referenced William Herschel’s calorific rays and Senebier’s photochemical experiments.69 Another report on Wedgwood surfaced in 1807, one by Biot in 1811, and another in an 1812 translation—more are likely to be found.70 This marked interest is connected with a strong uptick in studies of metallic compound photochemistry over the years 1808–1820 in Annales de chimie, the main journal for the field. In the 1809 introduction to the first edition in French of Thomas Thomson’s A System of Chemistry, Berthollet relates the experiments of Scheele, Ritter, and William Herschel.71 The same year, chemist Jacques-Étienne Bérard wrote an article on tin muriate and its photosensitive properties.72 In 1811, Étienne-Louis Malus, while theorizing polarization, gave a poor review of Goethe’s 1810 Theory of Colors, with the exception of the appendix by Thomas Johann Seebeck describing how to obtain silver chloride images of the solar spectrum.73 In 1813, Berthollet, Jean-Antoine Chaptal, and Biot reviewed Bérard’s set of publications, supporting his claims that the analysis of the effects of light on metallic compounds was now a central direction for optical research.74 Bérard’s results were published only later in 1817. His apparatus follows the standard setup with heliostat, darkroom, prism, and “paper treated with silver chloride,” while its prism came from “the superb cabinet of Mr. Charles,” suggesting that Charles himself may have been involved.75

Arago knew all these developments firsthand and was therefore among the most knowledgeable photochemists of the period. Neither John Herschel nor Arago invented photography, even though the former suggested in 1839 that the latter did in 1821. Yet both had the requisite optical, photochemical, and instrumental know-how; this is why Daguerre chose Arago as his champion in 1838. As soon as he heard of the daguerreotype, John Herschel retro-engineered photographic processes in a few days, offering improvements on the paper process within months.76 Why neither of them pursued fixed photographic processes earlier is not hard to guess. Their focus was the fast-moving and sprawling field of physical optics, in which a unifying theory seemed just around the corner. Both were committed to transparent science, criticizing Joseph von Fraunhofer in 1824 for keeping his superior glassmaking process a trade secret. Niépce, Daguerre, and Talbot, however, shared Fraunhofer’s commercial proprietary secrecy.

The earliest photochemical imaging experiments by Nicéphore Niépce date from 1816, neatly coinciding with the apex of photochemistry research in France. Yet Niépce was sufficiently unfamiliar with optics and photochemistry that when reporting on his first photosensitive print to his brother Claude, he marveled both at the camera obscura’s top-down inversion and the fact that the farm aviary he shot from his window appeared in photonegative. The brothers nonetheless caught on quickly. A few months later, Claude recommended “a solution of iron muriate” about which “he had read” (Bonnet and Marignier, Niépce, 1:407–8). The source is likely the 1813 issue of the Annales de chimie mentioning Bérard’s experiments with silver oxide photosensitivity and an article by Gay-Lussac on iron muriate. Nicéphore soon indicated he just read about guaiac resin dissolved in alcohol turning green when exposed to light, a reaction described in Thomson’s 1809 French edition of System of Chemistry, with a dedicated section on photochemistry. The book includes a sizable section on indigo, explaining why he would be familiar with it (Bonnet and Marignier, Niépce, 1:407–8).77 While the Niépce brothers suggested that their original insight about photography came from the time they were conscripted and stationed in Sardinia in 1797, they set out to devise a workable photographic process only in 1816 at the exact apex of French photochemical research. It is therefore reasonable to assume that the Niépce brothers were more aware of contemporaneous photochemistry research than they let on. The overlooked intermediaries between pre-photographic bricoleurs and scientists were Parisian instrument-makers, whom I examine after a brief but important detour through Talbot.

Talbot’s Internship with Arago at the Paris Observatory

Photography historians have consistently downgraded or overlooked the role of physical optics research in the emergence of working photography. A case in point is Talbot’s apprenticeship with Arago in 1825. After graduating from Cambridge in 1821, Talbot dabbled in chemistry, physics, and archaeology but began considering a career in astronomy.78 His notebooks of 1821 and 1822 are replete with astronomical observations, comet coordinates, computations of ellipses and parallax, and advanced algebra—an ad hoc training program.79 By 1822–1823, he knew Fresnel’s work on interferences, explored chromatic aberration, and made plans for constructing a photometer and a heliostat.80 In 1824–1825 he traveled to Paris and spent two weeks in March 1825 interning directly with Arago at the Paris Observatory. Talbot’s travel journals collect bits of Arago’s opinions, teachings, hypotheses, past research, and current investigations. For example, Arago explained to him why the constant speed of light among stars moving in different directions disproves the emission theory of light.81 In sum, it was a one-on-one seminar with the leading specialist in astronomy, optics, light, and photoimaging. Talbot does not mention photochemistry, yet he indicates: “Hook’s Micrographia [Arago] mentioned as a work too little known: he says the same explanation of the coloured rings is there to be found which Young afterwards imagined.”82 Young, we recall, made photochemical images of these diffraction rings in 1803. Talbot’s journal indicates that interference fringes and the WTL were topics he had discussed with Arago; there is little reason why Arago would not have shared with him his 1821 photochemical prints of interference fringes that confirmed the WTL.

Larry J. Schaaf, the leading expert on Talbot, conjectures that the latter’s interest in photochemistry dates only from 1831, after he (and Charles Babbage) witnessed experiments by John Herschel on platinum muriate exposed to sunlight. Schaaf trusts Talbot’s statement in The Pencil of Nature that failing to draw with a camera lucida at Lake Como in 1833 convinced him to turn to the camera obscura (Schaaf, Out of the Shadows, 36–37). Neither conjecture appears tenable. In early November 1827, John Herschel personally mailed Talbot his essay on “Light,” which became a standard in British optics for decades and marks John Herschel’s final conversion to the WTL.83 The essay states clearly: “Thus, a set of fringes formed by the interference of two solar pencils with a common origin, being kept very steadily projected for a long time on one and the same part of a sheet of paper rubbed with muriate of silver, a series of black lines became traced on it, the intervals of which were smaller than those of the dark and luminous fringes formed by homogeneous violet light.”84 This refers to Arago’s 1821 photochemical prints of interference fringes. Talbot certainly read Herschel’s essay very closely, and if he had not already learned of these experiments from Arago himself, he would have in John Herschel’s essay in 1827.85 As for the camera obscura, Talbot’s notebooks contradict his own statement about the 1833 date. One entry from summer 1829, about equipment for a mountain trek, mentions “shoes-gun-sextant-cam. lucida & obscura. English flora. 2 lorgnoles.”86 Neither Niépce nor Talbot, despite their claims to the contrary, worked in a vacuum outside of physical optics.

The Missing Link: Parisian Instrument-Makers

The inceptors of working photography—Niépce, Daguerre, Talbot—and astronomers and physicists at French research institutions depended heavily on an intermediary community that has gone largely unrecognized: instrument-makers. In large European cities in the late eighteenth and early nineteenth centuries, industrial, scientific, and educational needs for precision apparatuses caused a growth in specialized workshops producing new instruments.87 In Paris they concentrated around the Seine in the Latin Quarter, where the continental system as well as new research schools and institutions boosted the density and quality of their output from 1800 to 1820. By 1825, French commercial optics matched leading British firms and Fraunhofer’s lens-making process.88

Not only were instrument-making ventures highly concentrated and competitive, they were often familial establishments spinning up from or merging with each other. Physicist Jean Nicolas Pierre Hachette describes a microscope made by Charles Chevalier in 1825 as “a convex prism similar to that of the camera obscura which M. Vincent Chevalier made in 1819. . . . This prism, as M. Fresnel put it nicely in his report on the microscope of M. Selligue, serves both as mirror and magnifier. As for the diaphragms . . . we must in truth say that they were known and appreciated by the late M. Charles, as well as those who took the courses on optics from this excellent professor, among whom we can cite MM. Baillif, Dumotiez uncle and nephew.”89 This passage evidences intensive and reciprocal interactions between instrument-makers and scientists who commissioned, reviewed, and used their instruments.90 It also shows the pivotal role of Jacques Charles in training the Parisian instrument-making community. Conversely, employees at instrument shops often ran workshops for students or served as préparateurs (technical assistants) in course demonstrations and experiments (Blondel, “Electrical Instruments,” 164). The imbrication was so complete that catalogs of instrument-makers were referenced in or even printed within leading European scientific journals.91 When international scientists visited Parisian instrument-makers in the early decades of the nineteenth century, they sampled specialized devices and gathered information about the latest innovations and theoretical advances. Alessandro Volta, Michael Faraday, and Davy, for instance, all visited the Dumotiez firm in the early 1800s, while Talbot stopped at the Lerebours shop every time he came to Paris (Brenni, “19th-Century Scientific Instrument Advertising,” 508).

I want to focus on two instrument-makers germane to this study: Paul Gustave Froment and Vincent Chevalier. Froment graduated from École Polytechnique, where he had worked with Arago before constructing optical instruments and investigating photosensitive compounds. He made photochemical contact prints of leaves, feathers, and other semitranslucid objects, succeeding in “fixing” them in 1836 independently of Daguerre and Talbot.92 When Arago publicized the process of Daguerre, Froment went home and made a photochemical image the same day.93 Froment subsequently built a telegraph with a disk keyboard producing tracings on a clock-driven “strip of paper unreeling at uniform speed,” electrical wires for a telescope eyepiece for Arago, a chronograph, the official replicas of the meter, the wind turbine for the rotating mirror in Armand-Hippolyte-Louis Fizeau and Jean-Bernard-Léon Foucault’s apparatus measuring the speed of light, and Foucault’s famous pendulum (Laussédat, Notice biographique sur Gustave Froment, 14, 17–18, 20, 25). This array of devices, parenthetically, evidences the common formations of photocinema from the 1830s to the 1850s (see chapter 6).

Vincent Chevalier was the hinge figure in the implementation of photography: He worked directly with Arago, Charles, Niépce, Daguerre, and Talbot. In 1823, Chevalier released a meniscus-prism portable camera obscura that artists—including Daguerre—considered the best available. In the early 1820s, Vincent Chevalier and his father Charles Chevalier, together with several scientists including Jacques Charles, worked to procure flint-glass from England and devise new technics for making achromatic lenses.94 After confirming in a letter to Niépce in December 1825 that “your discovery . . . is of major importance,” in 1826 Vincent Chevalier suggested to Daguerre that he should meet Niépce since both were working on photochemical picturing (Bonnet and Marignier, Niépce, 1:733–34; Chevalier, Étude, 21). At that time, the Chevaliers were collaborating with Giovanni Battista Amici and Arago on optical lens design and assembly for telescopes. As for Talbot, it was Charles Chevalier who provided Talbot with optical components and camera obscuras (Chevalier, Étude, 146). These cursory indications of interactions between pre-photographers, astronomy and light physics researchers, and instrument-makers likely represent the tip of the iceberg. The tight interweaving of these three communities is still to be accounted for in the siloed historiographies of photography and cinema.