by Sarah Dry
Geikie was sanguine about the prospect of what we would call more interdisciplinary approaches to the big questions, with that of the ice age being most important. “As the circle of knowledge widens,” he wrote in his 1874 book The Great Ice Age, “boundary divisions become more and more difficult to determine. Perhaps of no physical science is this more true than that of geology. At one time the investigator into the past history of our globe had the field almost entirely to himself, and the limits of his study were as sharply defined as if they had been staked off and measured. Now, however, it would be hard to say on which of the territories of his scientific neighbors he must trespass most. He cannot proceed far in any direction without coming in contact with some worker from adjacent fields. His studies are constantly overlapping those of the sister sciences, just as these in turn overlap his.” This disciplinary crowding was, Geikie thought, itself proof of the ways in which all natural phenomena were knit together into a whole cloth. “It will, therefore, be a further proof of the unity of Nature, if those intricate problems which have hitherto baffled the geologist should eventually be solved by the researches of astronomers and the conclusions of physicists.”23
Among those who found much to agree with, and be stimulated by, in Croll’s theory was none other than John Tyndall. Given their shared commitment to physical reasoning, it’s little surprise they gave each other mutual encouragement. The two men corresponded, with the more conventionally successful Anglo-Irishman offering encouragement to the unknown Scot. Croll had come to his theory of global climate change directly after completing work on the behavior of heat in solids. Like Tyndall, his understanding of the forces at work on planetary scales was underpinned by an understanding of the physics of the molecular. Also like Tyndall, Croll was no great mathematician. Both relied on a rather astonishing intuitive feeling for the way physical forces interacted rather than a mastery of complex mathematics. Tyndall praised Croll’s use of a metaphor to describe the action of molecules: “your letter was interesting to me as an illustration of power to seize a definite physical image—the molecules acting as hammers was capital.”24 Tyndall embraced him as an intellectual fellow-traveler, a thinker who used images to make his points (and perhaps even to think with) and was unafraid to generate grand theories. “It is both amusing and interesting to me,” wrote Tyndall in another letter, on studies of heat, “to trace the parallelism which has run between your thoughts and mine on the subject.”25
While Croll remained resolutely fixed on the largest of scales—that of the entire planet—Tyndall made a career of moving between scales. He observed and generated theories about the very small, such as ice crystals and water molecules, and the very large, such as glaciers and mountains. Tyndall saw connections everywhere, but water in particular provided access to this central mystery, and beauty, of the universe: its continuity. It is strange but true, wrote Tyndall, that the “cold ice of the Alps has its origin in the heat of the sun.”26 He went on: “You cannot study a snowflake profoundly without being led back by it step by step to the constitution of the sun. It is thus throughout Nature. All its parts are interdependent, and the study of any one part completely would really involve the study of all.”27 For Tyndall, fundamental forces were never far removed from the largest scales of all. The tiniest changes that might occur in the deepest part of a glacier were connected not only to the entire glacier and its motions, but to the general physical properties at work everywhere on Earth and in the universe as a whole. Tyndall’s imagination did not stop at any point, but continued ever upward and outward, linking earthly physics to the physics of the sun and the cosmos in a chain of physical connection.
The idea that Nature was continuous—that energy and matter were linked in an uninterrupted chain of events—was for Tyndall a kind of secular religion. While he expressed his conviction in this continuity more loudly—and insistently—than many of his contemporaries, he was not alone in seeking to use the physics of the building blocks of matter to explain and understand the most complex, large-scale phenomena possible. Where previously, those who studied the earth had been content to try to map and describe what lay before them—as naturalists and as geologists—in the middle decades of the nineteenth century, it seemed increasingly possible to discover the mechanisms by which matter shaped the earth, to explain rather than simply describe terrestrial phenomena. Glaciers, then, were the perfect laboratory not only for testing ideas about the history of the earth but for helping transform the sciences of the earth. “No branch of study will place us in closer connection with the workings of nature,” wrote a reviewer on glacier writings by Tyndall, Agassiz, and Forbes, “or in a better position to observe how the most delicate physical elements combine to produce the most stupendous results, than that which concerns those vast masses of ice, the glaciers.”28 Glaciers helped reveal the internal actions of nature, to show how something as delicate as a crystal of ice could, when given enough time and alongside enough other crystals, change the shape of entire mountain ranges, and even entire continents.
Where Tyndall’s special skill lay was in showing how the discoveries yielded by the mountains could be extended by experiments done back in the laboratory. In the Alps, Tyndall measured the motion of ice flows that filled entire mountain basins. Back in London he could continue his studies of the motion of ice at vastly reduced scales. While Tyndall was motivated by a pointed desire to “destroy” the theories of those he saw as his rivals, it was in the to-and-fro between mountains and laboratories—rather than in the battle for the definitive theory of glacier motion—that he would make his greatest contribution.
His laboratory was located in a convenient spot in the basement of the Royal Institution, on Albemarle Street just off Piccadilly, where he gave public lectures in his role as professor of natural philosophy. In the summer of 1856, immediately following his first excursion to the mountains with Thomas Huxley, Tyndall had returned to his laboratory and started fooling around with ice, turning impervious river ice into fissured glacier ice, making the telltale blue bands he had witnessed on the glacier appear, forcing cleavage into transparent ice of almost crystalline perfection.
The experiments were beautiful in their simplicity. He had a laboratory assistant make a series of hard wood molds. He used them to shape and squeeze ice, to try to imitate the action of the glaciers. What he wanted to show was that ice moves through a stutter-step of freezing and melting that happens at such minute scales of both time and size that it is indistinguishable, in its results, from the flow of water. While ice seemed to act like a viscous liquid—like treacle or honey—according to Tyndall it really acted like a brittle substance. Under the cover of thousands of tons of glacier, the ice melted and refroze in tiny but discrete increments. Tyndall used an ugly word, originally his mentor Michael Faraday’s, to describe the process. Regelation. A series of alternating physical states, solid to liquid to solid, that occurred far beneath the surface, at the rough contact between the glacier and the earth. The special addition of pressure was a new twist provided by James and William Thomson. Together, the Thomsons predicted and then showed by experiment that pressure lowers the melting point of ice.29 This means that at the bottom of the glacier, where the pressure of untold tons of ice and snow lying above is greatest, the ice will melt. Meltwater will flow away from the glacier and, having thus lowered the pressure incrementally, the base of the glacier will refreeze momentarily until the pressure increases sufficiently to melt it again. And so the cycle will continue.
The hum of atoms that Tyndall believed enlivened every bit of the universe, seen and imagined, rose to a pitch beneath the ice. Far below the surface, the ice hovered, almost tenderly, at its melting point. Across that tender borderline, the ice fractured and healed itself repeatedly. It broke under its own pressure and mended under that same pressure, releasing heat in the form of water. What seemed fluvial was massive, skidding, a giant locomotive making its juddering way down to the valley
.
On January 15, 1857, Tyndall made the first of many presentations on his glacial research. In addition to presenting the theory he and his friend Thomas Huxley had developed together, Tyndall took the opportunity to attack the other leading theory of glacial motion of the day, that of James David Forbes. Forbes was older than Tyndall and had first traveled to the Alps, with Agassiz himself, fifteen years before Tyndall had. Forbes had gained the enmity of Agassiz after publishing a paper that the latter felt failed to credit him sufficiently. Undaunted, Forbes continued to travel to the Alps and publish papers based on the notion that the ice was, in fact, a viscous substance similar to treacle. Tyndall and Huxley attacked Forbes’s sloppy use of the term viscous. Tyndall asserted that when stretched enough, the ice would eventually turn brittle and snap. The viscosity that Forbes diagnosed was only apparent, not real, argued Tyndall.
Tyndall’s theory does not sound so very different, to modern ears, from that of Forbes. Both were convinced that ice flows like a liquid; they differed only in the details of how it flowed. The difference between them lay in the kinds of evidence they used to make their claims. For Forbes, the movement of glaciers was a matter of geology—of understanding the forces shaping the earth at the largest scales. The micro-physics of how, precisely, the ice flows was unimportant. For Tyndall, the matter was one that must be solved by physical reasoning. Drawing on work by Hopkins and the Thomson brothers, Tyndall suggested that the glacier was moving in increments. He admitted that these were tiny increments, consisting of miniscule amounts of ice that melted and refroze at the very depths of the glacier, but the point to be made was much larger. Ideas about molecules and energy that had been gleaned from mathematics and the most fundamental physical descriptions could be used to predict and to understand the behavior of the largest, messiest, and seemingly most inscrutable of things, the glaciers of the Alps. In this sense, the battlefield over which Tyndall and Forbes were tussling was very large indeed. Not simply a matter of semantics, it was a battle over the right to claim that a certain way of knowing the earth and a certain kind of explanation was more truthful than another.
Not everyone agreed with Tyndall’s version of science. Before agreement could be reached about the nature of the ice ages, the history of the earth, or the movement of glaciers, agreement had to be achieved on what an answer—a theory—might look like. Tyndall had tried to win the battle by linking his heroic exploits in the mountains to his disciplined experiments in the laboratory. In both cases, he suggested that he alone (despite the near-ubiquitous presence and contribution of assistants and porters) was capable of revealing the hidden truth of phenomena that seemed one way but really were another. In the case of the ice, the seeming flow of the glaciers was actually incremental regelation.
William Hopkins considered that both Tyndall and Forbes were each a bit right and each a bit wrong in their proposition of something they both called a “theory of glacial motion.” Too many of the “numerous discussions which have taken place during the last twenty years,” wrote Hopkins, were only partial and incomplete theories. What was lacking was a “complete and sufficient theory founded on well-defined hypotheses and unequivocal definitions, together with a careful comparison of the results of accurate theoretical investigation with those of direct observation.” What Hopkins wanted to call a theory was something that looked like physics—based on a well-defined hypothesis and absolute definitions—that also explained the phenomenon that had been observed by the geologists. As far as Hopkins was concerned, both Tyndall and Forbes were guilty of calling a total theory what was merely partial description of one of the ways a glacier could move. “The Expansion Theory ignored the Sliding Theory, though they were capable of being combined,” wrote Hopkins, “the latter theory was equally ignored by the Viscous Theory . . . [and] the Regelation Theory is not properly a theory of the motion of glaciers, but a beautiful demonstration of a property of ice, entirely new to us, on which certain peculiarities of the motions of glaciers depend.” The best and final theory, pointed out Hopkins, would be one that required no “qualifying epithet” to distinguish it from a rival claim.30
In making the move from the Mer de Glace to the laboratory, Tyndall was trying his best to come up with such a final theory. He was trying to forge a link between the geologists, such as Forbes, whose identities were bound up with muddy boots, sturdy instruments, and physically taxing expeditions to mountaintops and glacial fields, and the physicists, such as William Thomson and William Hopkins, who appealed to physics and mathematics to explain natural phenomena. Much of what Tyndall was doing in the Alps and in the laboratory anticipated later developments in the earth sciences that brought together mathematical physics and descriptive geological approaches.31 It would be wrong, though, to see Tyndall as fully modern. He was a qualitative rather than quantitative physicist. Analogy and metaphor were his tools, not mathematics. His most significant achievement was to link different ways of knowing. He brought together the experience of being on the glacier—the awe, the terror, and the particular insight into natural phenomena that it made possible—with the experimental investigations he did in his laboratory, a place from which awe, terror, and the specificity of landscape was expressly excluded. By doing both things—and calling both things “science”—he was staking a claim to what science might be.32
He performed a similar trick in his writing, drawing distinctions between different ways of knowing even as he brought the two together. His 1860 book The Glaciers of the Alps was divided cleanly into two parts.33 The first, which Tyndall called narrative, contained headings such as “Expedition of 1856” and “First Ascent of Mont Blanc, 1857.” The second, which he called science, contained such chapters as “light and heat,” “origin of glaciers,” and “the colour of water and ice.” Intimately related, the two were also best kept separate. “The mind once interested in the one,” Tyndall cautioned, “cannot with satisfaction pass abruptly to the other.”34 He knew almost instinctively how to keep an audience member or a reader engaged. “Once upon a steep hard slope Bennen’s footing gave way,” began one episode about an adventure he and his Swiss guide had on a descent from the summit of the Finsteraarhorn, “he fell, and went down rapidly, pulling me after him. I fell also, but turning quickly, drove the spike of my hatchet into the ice, got good anchorage and held both fast.”35 This was material designed to keep the attention of a young boy or man—Tyndall’s imagined (and it seems preferred) audience. Having captured it (and impressed the reader with his own stamina and bravery), Tyndall hoped to carry his readers with him into the more austere topics such as the curious veined structure of the glaciers or, more to the point, the mechanism responsible for their motion.
FIG. 2.7. The public enjoyed stories of daring exploits by the members of the Alpine Club, established just two years before this publication. From the title page of Peaks, Passes, and Glaciers, A Series of Excursions by Members of the Alpine Club (London: Longman, Brown, 1859).
The Glaciers of the Alps was a very popular book, selling many copies and bringing Tyndall firmly into the center of a fashionable circle of London intelligentsia. The public seemed to clamor more for stories of danger and heroism than they did of glacier motion, but on the whole, the idea that the search for knowledge motivated the risky feats made them seem more rather than less heroic. Just as John Franklin’s expedition in search of the fabled Northwest Passage (and those sent out subsequently to search for the lost ships) mixed national pride with the nobility of scientific exploration, so Tyndall’s work blended vicarious thrills with the cooler appeal of participating in the increase of scientific knowledge.
Tyndall’s scientific style wasn’t to everyone’s taste. A group of scientists found common cause in opposing him. He was, they thought, the worst possible combination: a dangerously unchristian show-off seriously lacking in mathematical skills. James Clerk Maxwell used the full force of his own literary sensibility to attack the Anglo-Irishman
, coining a term, “Tyndallize,” to refer to the theatrical manner in which Tyndall communicated. In an 1863 manuscript poem that was shared privately among the group of Tyndall skeptics, an anonymous author (almost certainly Maxwell) held little back:
There on a platform stood the fiend
His wide mouth grimaced in smile
Upon his right, the electric light
And on his left a [galvanic] Pile
And lo! The well dressed multitudes
Pressed forward in profusions
While scientific beggars sat
On the door of the Institution.36
In Maxwell’s biting poem, Tyndall becomes a grotesque caricature, as do his fashionable audiences and all those excluded from the spectacle. As if the point weren’t already clear, in his review of an essay by Tyndall in a popular magazine defending his theory of glacier motion, P. G. Tait commented that “Dr. Tyndall has, in fact, martyred his scientific authority by deservedly winning distinction in the popular field.”37
These sorts of exchanges make it clear that though Tyndall may have won the battle for the public’s attention, he had done so at the cost of alienating some of his scientific peers. His success at lecturing was not enough to win him victory in the matter of glacier motion. But nor, for that matter, did Forbes. The dispute between the two men over how glaciers moved was never resolved. Petty concerns about priority and citation mounted, and the whole debate degenerated into little more than name-calling.38 This was partly a result of the strong personalities involved, but it was also a measure of how much the debate was not about any theory in particular but, rather, about what counted as a theory. When the very boundaries of a problem are up for consideration, it is difficult, if not impossible, to recognize any given explanation as more complete than another.
