Perhaps fittingly for a man whose name was to become linked with the ice ages, James Croll was born on a cold, snowy January night in 1821, near the end of a time that is now known as “The Little Ice Age” (about which more will be said in chapter 11). But weather aside, there was little to indicate that this new entry into the world would make important contributions to our understanding of ice ages and climate. Croll was born in rural Scotland; his father was a crofter who also worked as a stonemason. It was a not an easy life. Although the family was by no means destitute, neither were there any luxuries. Young Croll was somewhat sickly, and only attended formal school classes intermittently. He was educated partly at home, sometimes tutored by his parents and at others by a local schoolteacher. But at least initially, he showed little real interest in learning. However, when he began to realize the possibilities that education offered, his attitude changed. Unfortunately, just at that time, at age thirteen, when he was finally eager to push on with his learning, he was forced to abandon further study. He was needed to work on his family’s small farm.
Croll’s change of heart about education seems to have come from a single incident in 1832, when he was eleven. It was characteristic of a number of events in his life that suddenly led him in new directions, often, it seems, on little more than a whim or passing impulse. The 1832 incident occurred on a visit to the nearby city of Perth, where the young Croll found the very first issue of a small periodical called the Penny Magazine in a bookshop. He promptly bought it, and was hooked—from then on he purchased issues whenever possible. The little journal was published by an organization that called itself “The Society for the Diffusion of Useful Knowledge,” and in the case of James Croll, it certainly succeeded in its aim. Although Victoria was not quite yet queen when Croll stumbled on that first issue, it was a magazine and a venture typical of Victorian Britain: eclectic, wide-ranging, and meant to bring information about the wider world to the British public. The issue that first caught young James’s eye in Perth contained, among other things, brief sketches of the lives of the French mathematician and philosopher René Descartes and the British physician who discovered the true nature of blood circulation, William Harvey; an article about Van Diemen’s land (now Tasmania); and a story about the grizzly bear that had just arrived at the London Zoo. Whether it was the illustrations or the titles that attracted Croll’s attention is unknown, but from what we know about his studious habits in later life, it is likely that he read every word in the slim, eight-page issue. For a country boy, it was a window onto lands beyond his own and a source of insight into the accomplishments of prominent intellectuals. It was almost certainly one of the major inspirations for his own intellectual endeavors. As a grown man, Croll went to some lengths to purchase a few missing back issues of Penny Magazine, which was then no longer published, so that he would own a complete set.
Stimulated by what he learned in Penny Magazine, but still tied down to work on the farm, Croll eventually purchased a few key books on philosophy and science and set to work to educate himself. By the time he was sixteen, he was well versed in a wide range of subjects—remarkably so, considering that for much of this time, his days were occupied with physical labor. Croll’s approach probably helped. He was to remark later that he was generally not interested in the small details of a problem, but instead wanted to understand the underlying principles. The details would fall into place if one knew the framework.
Croll eventually became a prominent figure in science and philosophy in Britain. It is difficult to know whether he would have been even more productive had he been able to attend university and live the life of a scholar. As it was, the path from a self-taught farm laborer of sixteen to recognition as a leading intellectual was long and tortuous.
The sixteen-year-old farm laborer reading books on philosophy in his spare time really wanted to attend university. But he had a very mediocre scholastic record and no formal training in Greek, Latin, or mathematics—important subjects for an aspiring university student in the nineteenth century. He also had no money. With characteristic logic and determination, although perhaps without pondering the consequences too carefully—another one of those new-direction-on-a-whim turning points in his life—Croll mulled over his situation for a few days and decided to become a millwright. It seemed to him to be an occupation that would fit his abilities perfectly. I know mechanics, he thought, therefore I’ll become a millwright. What he hadn’t considered was that his penchant for understanding principles rather than details meant that he knew mechanics from a theoretical point of view, but had little feeling for the practical side of machines. It must have been a rude awakening. But he persevered, served out an apprenticeship, and joined a local firm. “It was on the whole a rather rough life,” he reflected in his understated way. The work took him around the countryside repairing mill machinery, sleeping in “on an average, three different beds a week.” Bed is perhaps too luxurious a description for some of the sleeping arrangements Croll and his fellow mechanics endured; usually, they were put up in an unheated shed or barn. To add insult to injury, his employers were having a difficult time financially, and the employees were not always paid. After five or six years of slogging it out, he decided he had had enough and quit, resolving to try something else.
Croll was then twenty-one, unknown to anyone save a few farmers and millwrights in one small part of Scotland. He was still as unlikely a candidate to make major contributions to science as he had been at birth. It is all the more amazing, then, that when, in his sixties, Croll requested a small increment to his meager pension, a long list of luminaries from across the country petitioned to support his cause. The duke of Devonshire, the marquess of Salisbury, the duke of Buccleuch, Alfred, Lord Tennyson, Thomas Huxley, Joseph Lister, various members of Parliament, and many, many others lent their names to his request. It was a startling testament to his emergence as an original and influential thinker, especially as he had never been a part of the stratum of society occupied by most of his supporters.
After deciding to give up his chosen profession as a millwright, Croll, for the next sixteen years or so, worked variously as a carpenter, a tea merchant, a self-employed electric battery maker, a hotel manager, an insurance salesman, and a writer for a newspaper. None of these positions lasted very long, and they required him to move about from place to place in Scotland, and, at one point, to Leicester in England. During most of this time, the itinerant Croll read voraciously and systematically, concentrating on his twin loves of philosophy and science. He was much interested in the subject of will and the question of the existence of God. During a spell of unemployment when he was about thirty-five, he organized his thoughts on the matter and wrote a book: The Philosophy of Theism. Croll was still an unknown to those who pondered such matters, and he published the book anonymously, probably on the assumption that it was better to be anonymous than to be an unknown writer. Although he didn’t put his name on the book, he was otherwise not at all secretive about being its author. The year was 1857 and this was his first real venture into print. The subject matter wasn’t exactly likely to guarantee commercial success, and Croll had difficulty finding a publisher who was willing to take a chance on the book. However, in the end, it got good reviews. Although only five hundred copies were printed, Croll even earned a small sum in royalties. But perhaps the most important effect of this book was that it brought Croll recognition as a significant intellectual. He would no longer feel the need to publish his work anonymously.
A few years after his book appeared, in 1859, Croll’s meandering, frequently changing career finally settled into a semblance of normalcy when he took a position as caretaker at Anderson College, a private school and museum in Glasgow. No more hard manual labor, no more soliciting life insurance contracts from strangers, no more traveling about the country. Croll’s position required a minimal amount of effort, physical or mental, and his salary, although small, was sufficient for his needs. His brother, who was physic
ally disabled and lived with Croll and his wife, helped him with the work. The school had a well-stocked library, and the science section was extensive. Croll had plenty of free time; for a man who loved to read and think it was heaven. Almost forty, he was ready to begin making his mark in the field of science.
In his short autobiography, Croll recounts that when he took up his position at Anderson College, his primary intellectual interest was in philosophy and religion, the twin subjects of the book he had published a few years before. He had plans to expand his earlier exploration of these topics in a more systematic way. But instead he found the library at his new place of employment full of interesting works in science, and he decided to put his “metaphysics” aside for a while to investigate them. As a teenager, when he first began his program of self-education, he had been much taken with physics and mathematics. Through the newfound resources of the library at Anderson College, he wanted to reacquaint himself with these subjects, and to find out what was new in the world of science. He became especially interested in research into the nature of heat, electricity, and magnetism, and, quite amazingly, within a few years began to make original contributions to these subjects.
The list of Croll’s scientific publications begins in 1861, just two years after he began his caretaker’s job in Glasgow. His first effort was a paper on electricity in the respected Philosophical Magazine. Over the next twenty-five years, he contributed, on average, several articles annually to the scientific literature, many of them in the leading periodicals of the day. Although it was undoubtedly a time when a determined “outsider” could make more of an impact on the world of science than is possible in today’s specialized world, Croll’s record is nevertheless impressive. It is one that would bring credit to a full-time present-day academic.
Although Croll was retiring by nature, he had no hesitation in sending copies of his scientific papers to leading scientists throughout the country and corresponding with them about his work. He seemed secure in his scientific endeavors and confident in his own ability, in contrast to his feelings about some of his other ventures. Recognition of his work was rapid. In 1863, the prominent physicist John Tyndall, professor of natural philosophy at the Royal Institution in London, corresponded with Croll about some of the ideas expressed in his early publications. Tyndall urged him to continue sending papers, writing, “I have no doubt that anything you send me will interest me.”
At about this time Archibald Geikie, one of Scotland’s most prominent geologists, published a lengthy and detailed description of glacial features in the country, concluding that they must be the work of great ice sheets that had flowed across the land in the past. The work had been discussed in scientific circles in Scotland for several years before its formal publication, and, attuned as he was to current research in the physical sciences, Croll was undoubtedly well aware of it. Here was a challenging and important unsolved problem to which he could turn his attention. Croll thought initially that it would be a relatively straightforward task; “little did I suspect, at the time when I made this resolution [to investigate the causes of ice ages] that it would become a path so entangled that fully twenty years would elapse before I could get out of it,” he would later say in his autobiography.
Croll attacked the ice age problem in the same way he approached all of his work in science: through first seeking to understand the governing principles. He described this method in the introduction to his book Climate and Time, which was published more than a decade after he first became involved in the ice age debate. Writing about what he termed “The Fundamental Problem of Geology,” Croll notes:
We may describe, arrange, and classify the effects as we may, but without a knowledge of the laws of the agent we can have no rational unity. We have not got the higher conception by which they can be comprehended. It is this relationship between the effects and the laws of the agent, a knowledge of which really constitutes a science. We might examine, arrange, and describe for a thousand years the effects produced by heat, and still we should have no science of heat unless we had a knowledge of the laws of that agent. The effects would never be seen to be necessarily connected with anything known to us; we could not connect them with any rational principle from which they could be deduced à priori [sic]. The same remarks hold, of course, equally true of all sciences, in which the things to be considered stand in the relationship of cause and effect. Geology is no exception.
Croll’s words could profitably be taken to heart by some scientists today. They show quite clearly why he was so successful as a scientist: he was not content to tabulate observations, or even, as Agassiz did, to synthesize them into a theory, without first trying to understand the underlying principles. In the case of glaciation and ice ages, he recognized that a major determinant of climate is the amount of heat energy the Earth receives from the sun—that had to be, in his terminology, one of the “agents” of climate. He also knew that the heat received from the sun varies because of the constantly changing orbit the Earth follows in its travels around the sun, and he made those variations the centerpiece of his investigation.
Croll was not the first to attempt to relate climate to the effects of the Earth’s variable orbit, but he was the first to put the theory on a firm scientific footing. The idea had actually been discussed on and off for almost a century before Croll entered the debate. By the 1850s, a section on “Astronomical Causes of Fluctuations in Climate” was even included in Charles Lyell’s widely read Principles of Geology, generally considered to be the first true textbook of geology, then in its ninth edition. In his book, Lyell summarized the evidence that had been accumulated up to that time, but he remained lukewarm about the possibility that astronomical influences were important. However, he did suggest that someone should carry out the laborious calculations that would be necessary to fully investigate this possibility.
Prior to Croll’s work, a few scientists had looked into the mathematics of the Earth’s orbital variations, but those who had thought about the implications for climate had concluded that the changes would not be of much consequence. They had considered the fact that the Earth’s orbit around the sun is not circular, but is actually an ellipse, with the sun located at one of its two foci, slightly offset from its center (see figure 9). This means that as the Earth makes its yearly journey around the sun, it is sometimes closer (and thus receives more solar energy) and sometimes farther away. It was also known that the shape of the elliptical orbit changes over time, from being almost circular at some times to much more elliptical at others. Such changes are formalized in the concept of eccentricity—the more elliptical the orbit, the greater the eccentricity. Changes in eccentricity affect the amount of solar energy received by the Earth at various points in its orbit—when the orbit is almost circular, the energy received is almost constant throughout the year; when the orbit is more elliptical, the variation between times of closest and farthest approach is much greater. But calculations showed that when averaged over a year—one complete revolution of the Earth around the sun—the differences resulting from these variations are negligible. Few believed they could be responsible for ice ages. There was an exception, however. In 1842, Joseph Adhémar, a French scientist, wrote a book titled Révolutions de la mer, in which he proposed that the combined effects of eccentricity and the tilt of the Earth’s axis of rotation play an important role in glaciation.
Figure 9.Plan (above) and side (below) views of the Earth’s orbit around the sun. The eccentricity of the orbit is much exaggerated, and the sizes of Earth and sun are not to scale. As the eccentricity changes, the orbit becomes either more or less elliptical. The tilt of the Earth’s axis of rotation is shown in the side view. At present, the Northern Hemisphere is tilted toward the sun in June, when the Earth is distant from the sun.
Because the details of the Earth’s orbit are important for understanding the arguments made by Adhémar, Croll, and others about glaciation, it is worth pausing briefly to consider them more care
fully. Without perturbing influences, the orbit of the Earth around the sun would be unchanging. But due to gravity, each planet has an effect on the orbits of the others. And because the planets orbit the sun on different timescales, their relative positions, and therefore their influences on one another, are constantly changing. Thus the shape of the Earth’s elliptical orbit—its eccentricity—is also continuously changing. These changes are slow and regular, and they can be calculated. Over long periods of time, the Earth cycles through the same orbital conditions over and over again. With computers and accurate knowledge of the masses of the planets, it’s possible to plot out the Earth’s orbit, and those of the other planets, very accurately far into the past or the future. These kinds of calculations are routine for NASA engineers—when they launch an exploratory spacecraft to another planet, they have to know precisely where the Earth is in relation to other bodies in the solar system and where the target planet will be several years later when the spacecraft reaches it. The very first calculations of the planetary orbits, a truly monumental achievement in applying Newton’s gravitational theory to the solar system, were made by the French mathematician and astronomer Pierre-Simon Laplace in 1773. By the time Croll tackled the problem, the elliptical shape of the Earth’s orbit was well known, and it was also known that the eccentricity gradually changes. However, no one had yet done the systematic calculations to determine exactly what these changes were over very long periods of time.
Frozen Earth: The Once and Future Story of Ice Ages Page 10