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Charles Lyell and climatic change: speculation and certainty

JAMES RODGER FLEMING Science, Technology and Society Program, Colby College, Waterville, ME, 04901, USA

Abstract: In the first edition of the Principles of , announced his theory of the geographical determination of climate and speculated on possible climatic changes during the geological and historical past. In light of the subsequent discovery of ice ages, the proliferation of theories of climatic change, and the great climate debates of his time. Lyell's theory remained remarkably stable. This paper examines Lyell's appropriation, modification and rejection of the views of his contemporaries. It provides perspectives on elite and popular ideas of climate and climatic change from the late eighteenth century to 1875. examines Lyell's position on climatic change in geological and historical times, and explores in some detail the mutual influences of Lyell and , the proponent of an astronomical theory of ice ages.

I have often told (and been told) humorous stories positions created and defined? The answers are about climate and human affairs. This one, from varied and worthy of extended reflection. In the 1865, comes from a letter to Lyell from John absence of means to observe the climate system in Carrick Moore, FRS, field and long-time its entirety, (as an astronomer might view a star or member of the Geological Society. Moore writes: planet) or to experiment on it directly (as a chemist might view a reaction), how did scientific under- I fear you have not time to read the Reader, I standing of it emerge? must call your attention to the last number, in One approach, popular in the eighteenth century, which there is a true story of a Physician who was through appeals to authority-references to warned a Unitarian preacher that he would make historical literature, first impressions of explorers no proselytes in Northern Virginia because the or the memory of the elderly. This was the people all had fair complexions and therefore rhetorical strategy of Enlightenment writers who were Calvinists. If he wished to preach against wanted to support a particular theory of cultural the eternity of punishment, he should go to the development or decline. I will say more about this Hill Country. A map of the world is evidently shortly. much wanted to show the influence of Climate Another way of approaching the issue was to on Creeds, with contour lines-[Buddhism] collect massive amounts of meteorological data below the 50 foot level, Calvinists near the Snow over large areas and extended time periods in the line, and Papists principally on the Volcanic hope of deducing climatic patterns and changes. tufts... (J. C. Moore to C. Lyell, 5 March 1865 in Individual observers in particular locales dutifully Lyell papers) tended to their journals, and networks of cooper- So you see, climate is not only a complicated ative observers gradually extended the frontiers of issue, it is also a cultural one; even more so for meteorology. Although many of the basic meteoro- climatic change. logical instruments were invented in the seven- teenth century, they were not standardized or widely distributed until well into the mid-nine- Apprehending climatic change teenth century. In pursuing historical research on climate change, I During Lyell's lifetime, meteorology emerged as have had to ask several crucial questions. How do an organized, if not yet fully disciplined, obser- people (scientists included) gain awareness and vational science. Observations were tabulated, understanding of phenomena that cover the entire charted, mapped and analysed to provide represent- globe, and that are constantly changing on time- ative climatic inscriptions. This process profoundly scales ranging from geological eras to centuries, changed climate discourse and established the decades, years and seasons? How was this foundations of the science of climatology (Fleming accomplished by individuals immersed in and sur- 1990). National weather services were established rounded by the phenomena? How were privileged in Europe, Russia and the United States in the third

FLEMING, J. R. 1998. Charles Lyell and climatic change: speculation and certainty, hz: BLUNDELL, 161 D. J. & SCOTT, A. C. (eds) Lyell: the Past is the Key to the Present. Geological Society, London, Special Publications, 143, 161-169. Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

162 J.R. FLEMING quarter of the century, and by 1872, within Lyell's Montesquieu's ideas on climate and governance, lifetime, regular meetings were being held of the 's ideas on recent climate change in the directors of national weather services (Fleming Americas, and of course, generations of colonial 1997). settlers and revolutionary patriots (Fleming 1998). A third approach to privileged knowledge was to As late as 1779 - in other words in the prime of establish from first principles what the climate Hutton's life- the EncyclopdFdie of Diderot and ought to be and how it ought to change. Joseph D'Alembert still defined 'climat" in the ancient Fourier, John Tyndall and James Croll, to name but way, geographically, as a 'portion or zone of the a few, engaged in such speculative and theoretical surface of the , enclosed within two circles practices. These approaches-based on mathe- parallel to the equator', within which the longest matical, physical and astronomical principles- day of the year on the northern and southern tended to be most satisfying to those scientists boundaries differs by some quantity of time, for working within a particular disciplinary per- example one half hour. The Encyclopd(die spective; most only grudgingly admitted other provided a medical definition of climate as well, possible secondary causes of climate change. Lyell, understood primarily through the effects of climate of course, had his own favourite causal mechanism on the health and well-being of the inhabitants of which was solidly grounded in geological field various climes. It also mentioned Montesquieu's evidence. position on the influence of climate on people's In the twentieth century, climatic phenomena mores, character and forms of governance (Diderot have been rendered three dimensional by the & D'Alembert 1751-1765). development of upper-air observations, extended With no established science of climatology, into the indefinite past by palaeoclimatic authors such as Du Bos, Montesquieu and Hume techniques and, finally, globalized in the era of appealed directly to cultural sensibilities and satellite remote sensing. Many climate scientists prejudices, the authority of their positions residing today are working on links between remote sensing in their considerable literary skills and the lack of and more sophisticated computer models. They are other evidence to prove them wrong. Collectively, hoping, through advances in technology, to provide they generated a powerful vision of the climates of new privileged positions. For most scientists the Europe and America, shaping the course of empire goal is better understanding of climate: for some it and the arts: the concerted efforts of innumerable is also prediction and, ultimately, control. I might individuals in turn shaping the climate itself. By the add that an additional strategy for claiming end of the century, physiocrats had come to the privileged knowledge is the consensus method, for following general conclusions on climate change, example as currently practised by the culture and cultivation: Intergovernmental Panel on Climate Change (IPCC I. Cultures are determined or at least strongly 1995). shaped by climate. 2. The climate of Europe had moderated since ancient times. Perceptions of climatic change in the 3. These changes were caused by the gradual eighteenth century clearing of the forests and by cultivation. 4. The American climate was undergoing rapid and Climate-from the Greek term klima, meaning dramatic changes caused by settlement. slope or inclination-was originally thought to 5. The amelioration of the American climate depend only on the height of the Sun above the would make it more fit for European-type horizon, a function of the latitude. A second civilization and less suitable for the primitive tradition, traceable to , linked the quality native cultures. of the air (and thus the climate) to the vapours and exhalations of a country. The Hippocratic tradition This was the dominant popular understanding of further linked climate to health and national climate at the dawn of the nineteenth century character. Enlightenment ideas linking climate (Fleming 1998). change and culture were grounded in the work of the diplomat, historian and critic Abb6 Jean- LyeU's position Baptiste Du Bos, perpetual secretary of the French Academy, who argued that the rise and fall of In the first edition of his creative genius was not due primarily to 'les causes (1830-1832), Charles Lyell announced his theory morales' (education, cultivation, governance), but of the geographical determination of climate: a was largely attributable to changes in 'les causes theory that influenced generations to follow, physiques' (the nature of the air, land, soil and including G. E Wright (1889), M. Ramsay (1909- especially, climate). These ideas influenced 1910), and C. E. R Brooks (1926). He syste- Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

CLIMATIC CHANGE 163 matically rejected catastrophic agents of climatic changes were theorized to account for animal change, arguing patiently, systematically and migration and evolutionary changes as animals forcefully, as Martin Rudwick has recently adapted to different climates. Lyell concluded: reminded us, that 'modern causes', acting at their 9 the remains both of the animal and vegetable present intensities, were 'entirely adequate' to kingdom preserved in strata of different ages, explain the evidence of the past (Rudwick 1990). indicate that there has been a great diminution of Lyell also maintained that geology should remain temperature throughout the northern hemisphere, independent of cosmogony, just as history had been in the latitudes now occupied by Europe, Asia, divorced from myths of human origins (Bailey and America. The change has extended to the 1962). For Lyell, the geographical arrangements of Arctic circle, as well as to the temperate zone. oceans and continents, currents and winds were The heat and humidity of the air, and the sufficient to explain the immense variety of uniformity of climate, appear to have been most climatic zones being revealed by meteorologists, remarkable when the oldest strata hitherto such as , and scientific discovered were formed. The approximation to a travellers, such as . As climate similar to that now enjoyed in these Lyell perceptively noted, the ocean tempered the latitudes, does not commence till the era of the climate, 'moderating alike an excess of heat or formations termed , and while the cold', while elevated land, extending into the colder different tertiary rocks were deposited in suc- regions of the atmosphere, 'becomes a great cession, the temperature seems to have been still reservoir of ice and snow, arrests, condenses, and farther lowered, and to have continued to congeals vapour, and communicates its cold to the diminish gradually, even after the appearance of adjoining country'. Lyell made additional per- a great portion of existing species upon the earth. ceptive comments on the role of particular large- (Lyell 1830-1832, p. 103). scale features such as the African continent- "an immense furnace' that distributes its heat to Asia Lyell rejected, however, the notion of a secularly and Europe- and ocean currents such as the Gulf cooling Earth. Six years earlier, in 1824, Joseph Stream- which 'maintains an open sea free from Fourier had determined that the internal heat of the ice in the meridian of East Greenland and Earth had decreased no more than 3/100 of a degree Spitzbergen' (Lyell 1830-1832). during the course of recorded history (Fouvier Lyell used his climate theory to demonstrate that 1824). Instead, Lyell fixed his thoughts on gradual the past history of the Earth was 'one uninterrupted processes occurring steadily and repeatedly at the succession of physical events, governed by the laws Earth's surface-"on the connection at present now in operation' (Wilson 1972). Such a position between climate and the distribution of land and assumes that know all the laws currently sea; and if we then consider what influence former in operation- a precarious assumption in 1830 or fluctuations in the physical geography of the earth even today. Nevertheless, if it is accepted, Lyell's must have had on superficial temperature, we may position has important implications. Over immense perhaps approximate to a true theory' (Lyell geological time, in this view, gradual processes 1830-1832, p. 105). shaped the distribution of land and sea, which in For Lyell, the driving forces of climatic change turn determined the climates of the world. The were due to continuous changes in the distribution geographical distribution of species, which depends of land and sea: greatly on the climate and geographical conditions, When land is massed in equatorial and tropical was thus shaped by natural laws. In Lyell's termin- latitudes polar climates are mild. The land, ology, 'transportations of climate' contributed to heated to an excess under the equatorial sun, 'local extermination of species', while other gives rise to warm currents of air that sweep species better suited to the new conditions event- north. On the other hand, land massed around the ually took their places (Bailey 1962). poles produces the reverse effect. There is no Lyell introduced a substantial amount of land at the equator to soak up heat and no warm evidence indicating that the climate of the northern winds coming into polar regions. hemisphere was 'formerly hotter'. He included proofs from analogy derived from extinct quad- Lyell challenged his readers to imagine the rupeds; and direct proofs from the organic remains Himalaya Mountains, 'with the whole of of the Sicilian and Italian strata, from fossil remains Hindostan', sinking down and being replaced by in Tertiary and Secondary rocks and from the plants the Indian Ocean, while an equal extent of of the coal formation. He argued that the climate of mountainous lands rose up, extending from North Siberia and other Arctic regions had been formerly Greenland to the Orkney Islands. He pointed out temperate, but had become subjected to 'extremely that under such altered circumstances "it seems severe winters' due to changes in landforms. These difficult to exaggerate the amount to which the Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

164 J.R. FLEMING climate of the northern hemisphere would now be He admitted, however, that in certain locations 'the cooled down'. Lyell's imagined refrigeration, labours of man have, by the drainage of lakes and however, did not stop there. Icebergs would find marshes, and the felling of extensive forests', their way into southern waters, their melting caused minor changes in the climate system (Lyell creating vapour, fogs and clouds that would reduce 1830-1832). Waxing speculative (and realizing he solar insolation by half, causing the Earth to cool was doing so), Lyell explored the possibility of further, wrapping large portions of the northern future climatic influences caused by the progressive hemisphere in a 'winding sheet of continental development of human power, 'or perhaps by some ice'-a phrase of ominous significance for the other new relations, which may hereafter spring up organic world. When in the course of geological between the moral and material worlds' (Lyell time, conditions had reversed and continents again 1853). He did not speculate, however, on what dominated the equatorial regions, snow would be a these relations were. Nor did he venture an opinion, rarity, the Earth's crust would be heated to con- for example, on the recent rise of industrial power. siderable depths, and springs and surface waters Undoubtedly, many other aspects of Lyell's would run hotter, even in the winter (Lyell climate arguments constituted gross speculation. 1830-1832). For example, as Patrick Boylan reminds us (this In pondering the vicissitudes of climate, Lyell volume), in 1840 Lyell briefly joined forces with made the following four assumptions, quoted here and in decidedly from the eleventh (1872) edition of the Principles. non-uniformitarian speculations on glaciation. I cite the last edition published in his lifetime Another example comes from Lyell's well known because Lyell's principles remained basically maps 'showing the position of land and sea which unchanged from the first edition. might produce the extremes of heat and cold in the climates of the globe' (Fig. 1). I shall assume, 1st, that the proportion of dry These maps appear in all eleven editions of the land to sea continues always the same. 2ndly, Principles published in Lyell's lifetime. The maps That the column of the land rising above the depict, recognizably, the seven current continents level of the sea is a constant quality; and not only all bunched up near the equator to represent that its mean, but that its extreme height, is liable 'extreme of heat', and then shifted to polar regions only to trifling variations. 3rdly, That on the to represent 'extreme of cold'. Of course, there was whole, and in spite of local changes, both the no discussion of a possible mechanism to cause mean and extreme depth of the sea are such '.' Lyell added a note in the invariable; and 4thly, That the grouping together ninth edition saying, 'These maps are intended to of the land in continents is a necessary part of the show that continents and islands having the same economy of nature. (Lyell 1872, p. 264). shape and relative dimensions as those now E E Cunningham found it astonishing that 'Lyell existing, might be placed so as to occupy either the could consider it consistent with his "uniformity" equatorial or polar regions' (Lyell 1853, p. 111). that in recent times there had been a large rise of sea While this exercise resembles nothing more than a level and an even more recent withdrawal of the sea child's map game, the result is spookily familiar in of similar dimensions' (Cunningham 1990). What the contemporary era of plate tectonics. Cunningham found unusual-what he called a By 1853 Lyell had examined and rejected the 'catastrophic fluctuation' in sea level - Lyell would notion that changing sunspot abundances, as surely have explained, in accordance with his four reported by Schawbe and Sabine, had any influence principles, by a rearrangement of continents and on climate (Lyell 1853). In 1861 John Tyndall oceans, and a gradual yet dramatic local (but not began to popularize the results of his experiments mean global) increase in the depth of the sea. on the absorption of radiant heat by gases. He noted As described earlier, it was widely held that that changes in the amount of any of the radiatively humans might have altered the climate of the Old active constituents of the atmosphere-water and New Worlds by clearing the forests and vapour, carbon dioxide, ozone and hydrocarbons- cultivating the fields. Lyell was dismissive of such could have produced 'all the mutations of climate notions, in particular that climate had changed which the researches of geologists reveal.., they much for any reason in historical times; he constitute true causes, the extent alone of the considered the time period 'insufficient to affect the operation remaining doubtful' (Tyndall 1861). leading features of the physical geography of the Neither Tyndall nor anyone else pursued this globe'. Lyell acknowledged popular perceptions of hypothesis, however, until the turn of the century the variability of the seasons, but cited recent (Fleming 1998). Lyell's biggest challenge came in analyses of long series of meteorological 1864, when James Croll introduced his astro- observations which indicated the relative constancy nomical theory of the glacial epochs. As J. C. of the mean temperatures of particular locations. Moore wrote to Lyell in March 1865, 'Who would Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

CLIMATIC CHANGE 165 have thought fifty years ago, after astrology had 'On the physical cause of the change of climate gone out of fashion, that the stars were to enlighten during geological epochs'. In this paper Croll intro- us upon what is going on here.' (Lyell papers). duced revolutions in the Earth's orbital elements as likely periodic and extraterrestrial mechanisms for Lyell, Croll and the glacial epoch initiating multiple glacial epochs. Inspired by the R~volutions de lamer of Joseph James Croll (1821-1890), proponent of an Adh~mar (1842), and employing the calculations of astronomical theory of ice ages, was a self- Leverrier and Lagrange for the maximum educated Scotsman who was employed, after 1867, eccentricity of the Earth's orbit, Croll proposed that by the Scottish Geological Survey. The outlines of this 'eccentricity was sufficiently great to account his life are well documented in his touching auto- for every extreme of climatic change evidenced by biography, a chronicle of poverty, physical suffer- geology' (Irons 1896). Croll's theory of ice ages ing and neglect (Irons 1896). In 1864, Croll took into account both the precession of the published a paper in the Philosophical Magazine equinoxes and variations in the shape of the Earth's

Fig. 1. Maps showing the position of land and sea which might produce the extremes of heat and cold in the climates of the globe. Top: Extreme heat occurs when land masses are concentrated near the equator. Bottom: Extreme cold occurs when land masses occupy polar regions. (From Lyell 1853, p. 111.) Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

166 J.R. FLEMING orbit. It predicted that one hemisphere or the other ations of land and sea from direct accounts and would experience an ice age whenever two con- observations; the effects of varying eccentricity had ditions occur simultaneously: 'a markedly elongate yet to be proven (Lyell to Herschel, 11 February orbit, and a winter solstice that occurs far from the 1865, in Herschel papers). Lyell conducted a sun' (Imbrie & Imbrie 1979). Croll rejected two similar correspondence with the Astronomer Royal, astronomical notions of climate change: that the Sir George Biddell Airy, concerning the 'ancient Earth had passed through hotter and colder regions state of the Earth's orbit' (Airy to Lyell, 27 March of space and that the Earth's axis had shifted. He 1865 in Lyell papers). assumed only the well established variations in In response to Lyell's queries, J. C. Moore orbital excentricity and the obliquity of the ecliptic. responded: This provided a mechanism for multiple glacial The more I think of it, the more I feel puzzled to epochs and alternating cold and warm periods in understand how Astronomic causes can give us each hemisphere. In other words, when the northern the conditions required for glaciation. Mr. C[roll] hemisphere was in the grips of an ice age, the talks of cold periods, but a winter of -17 ~ F southern hemisphere would be in an interglacial. As followed by a summer of +119 ~ F is not what I the Earth's orbital elements varied, this situation should call a cold but an extreme climate .... would eventually be reversed. This potentially [There is nothing on the Globe which approaches serious challenge to the geographical theory caused such a state ] ... I cannot believe in these mon- an uproar among Lyell and his associates. strous results, and I think, as I suppose you do, In 1864, as he was preparing the important tenth that a vast extension of land about the S. Pole is edition of his Principles (1866-1868), Lyell sought at the bottom. (Moore to Lyell, 20 April 1865 in expert advice on how to deal with the new Lyell papers). contender. He asked Sir 's opinion on the reliability of Croll's 'facts and reasons', adding: By 1866 Lyell, on the advice of Herschel and Airy, had tentatively accepted Croll's theory as a Of their applicability to Geology I may perhaps true, but minor cause of climatic change. He wrote form an independent opinion .... I feel more than to Darwin: ever convinced that changes in the position of land & sea have been the principle cause of past ... the whole globe must at times have been variations in climate, but astronomical causes superficially cooler. Still, during extreme excent- must of course have had their influence & the ricity the sun would make great efforts to question is to what extent have they operated? compensate in perihelion for the chill of a long winter in aphelion in one hemisphere, and a cool Lyell also perceptively noted what was to summer in the other. become a fatal flaw in Croll's theory- that, according to the geological record, the glacial Lyell also incorporated into his explanation periods of the southern hemisphere coincided with aspects of Tyndall's work on radiative transfer, those of the northern, which would not be the case noting that plants requiring heat and moisture could if the eccentricity of the orbit were the controlling be saved from during an ice age 'by the factor (Lyell to Herschel, 31 January 1865 in heat of the earth's surface, which was stored up in Herschel papers). Herschel replied that perihelion, being prevented from radiating off astronomical causes could provide huge freely into space by a blanket of aqueous vapour temperature fluctuations, 'quite enough to account caused by the melting of ice and snow'. Here he for any amount of glacier and coal fields' (Herschel was grasping at straws, aware of new theoretical to Lyell, 6 February 1865, copy in Herschel problems, but taking from them only the aspects papers). that reinforced his own preconceptions. Lyell's letter to Darwin concluded: Suppose a distribution of land favorable to cold, suppose an extreme e[xcentricity], and suppose But though I am inclined to profit by Croll's the aphelion to coincide with the winter first in maximum excentricity for the glacial period, I one hemisphere and then in the other, and any consider it quite subordinate to geographical amount of glacier you can want is at your causes or the relative position of land and sea and disposal... (Herschel to Lyell, 15 February 1865, abnormal excess of land in polar regions. (Lyell copy in Herschel papers) to Darwin, 1 March 1866, in Darwin & Seward 1903) Lyell was very serious about this issue and responded with a 22 page letter to Herschel By this time Darwin had adopted Croll's explaining why geographical causes had to pre- conclusion that 'whenever the northern hemisphere dominate over astronomical ones. He knew the passes through a cold period the temperature of the enormous influence on climate of varying configur- southern hemisphere is actually raised'. He gently Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

CLIMATIC CHANGE 167 teased Lyell, pointing out that he had generally subsequent editions devoted more than twice as been a 'good and docile pupil', but he could not much space to climatic change. While the ninth believe 'in change of land and water being more edition had had about 58 pages on climate and its than a subsidiary agent' of the glacial period vicissitudes, the tenth edition had 130 pages, (Darwin to Lyell, 8 March 1866 in Darwin & including a new chapter on astronomical influences Seward 1903). Darwin also agreed with Croll that with a 37 page section on Croll: the advocates of the iceberg theory (Lyell) had formed 'too extravagant notions regarding the Mr. Croll's suggestion as to the probable effects potency of floating ice as a striating agent', and that of a large excentricity in producing glacial the 'scored rocks throughout the more level parts of epochs is fully discussed, and the question is the United States result from true glacier action' entertained whether geological dates may be (Darwin to Croll, 24 November 1868, in Darwin & obtained, by reference to the combined effect of Seward 1903). Of course Darwin's old nemesis, astronomical and geographical causes. (Lyell Agassiz, was still actively pursuing his defeat with 1866-1868, vol. 1, viii). the argument that extensive glaciation, in the equatorial Amazon valley and over the entire Lyell had complimentary things to say about continent of North America, would have prevented Adh~mar's Rdvolutions de la mer, even though the descent of any terrestrial life form from the most contemporaries considered it to be extremely Tertiary period (Darwin to Lyell, 8 September speculative, not to mention catastrophic in its view 1866, in Darwin & Seward 1903). of dramatic oceanic flooding. According to Lyeli, In September 1866, Croll received Lyell's proof Adhbmar 'called attention to a vera causa hitherto sheets for the climate chapters of the tenth edition neglected' (the precession of the equinoxes) and of the Principles (Croll to Lyell, 24 September reopened the question of historical climate changes, 1866 in Lyell papers). After seeing Lyell's for example in understanding the advance of the summary of his theory, which was fair but non- Swiss glaciers since the thirteenth century. Lyell committal, Croll wrote back immediately that he added that Croll's primary mechanism - changes in had altered his position considerably in his latest the eccentricity of the Earth's orbit-was also a manuscript. Croll now argued that the glacial epoch vera causa and could result in a 20 per cent could not possibly have been caused directly by any reduction or augmentation of the entire heat the change in the eccentricity of the Earth's orbit, but Earth received from the Sun. by the combined physical effects of 'certain Upon this difference of heat Mr. Croll has agencies which were brought into operation by founded a theory which attempts to account for means of the change' (Croll to Lyell, 28 September former changes of climate by the tendency which 1866 in Lyell papers). For example, an early edition a maximum excentricity would have to exagger- of Herschel's Astronomy pointed out that the ate the cold in that hemisphere in which winter amount of direct heat received by the Earth over the occurred in aphelion. (Lyell 1872, p. 277) course of a year is independent of eccentricity. However, Croll pointed out in letters to both Lyell Lyell concluded his review of Croll's theory by and Herschel that the climate would not be so pointing out that precession of the equinoxes would independent because of the latent heat effects of cause the alternate glaciation of only that hemi- snow cover (Croll to Lyell, 23 April 1866 in Lyell sphere in which winter occurred at aphelion. As a papers). This is just one example of the ways consequence, Croll had supposed that a vast ice cap Croll's rough calculations and constant modifi- on one side of the Earth 'would so derange the cations of his theory to incorporate geographical earth's centre of gravity as to draw the ocean feedback served to keep Lyell from dismissing the towards that pole, and cause the submergence of astronomical theory altogether. Croll received the part of the land'. The depth of the submergence he first volume of the tenth edition of the Principles in supposed was on the order of 500 feet. Lyell November 1866 (Croll to Lyell, 30 November 1866 pointed out to Croll that sea level would be lowered in Lyell papers). He thanked Lyell for the handsome during a glacial epoch, since an enourmous amount gift and for the 'highly complimentary way' in of ocean water would now be deposited as snow on which his astronomical theory had been treated. the ice cap (Croll to Lyell, 6 January 1866 in Lyell Lyell had agreed with Croll on many points. papers). Croll stuck to his theory, which was in fact Although they still had deep disagreements, Croll derived from Adhemar, but corrected his attributed their differences to basic incom- calculations to show that sea-level rise (in the patibilities in the approaches of physics and northern hemisphere only) would be 500 feet minus geology (Croll to Lyell, 12 December 1866 in Lyell the amount subtracted to build the continental papers). glaciers (Croll to Lyell, 16 January 1866 in Lyell Compared with previous editions, the tenth and papers). Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

168 J.R. FLEMING

Lyell faulted Croll for not paying sufficient References attention to abnormal geographical conditions. He ADHI~MAR, J. A. 1842. Rgvolutions de lamer, deluges pointed out that astronomical causes alone could periodiques. Carilian-Goeury & Dalmont, Paris. not account for the storing up of ice when deep BAILEY, E. 1962. Charles Lvell. Nelson, London. oceans prevailed at both poles. He further noted BROOKS, C. E. P. 1926. Climate through the Ages: A Study that during extreme eccentricity, the minor axis of of the Climatic Factors and Their Variations. R. V. the ellipse would be shortened, causing the amount Coleman, New York. of heat received from the Sun to exceed its present CROLL. J. 1864. On the physical cause of the change of value, working against the formation of a glacial climate during geological epochs. Philosophical period. He rested his case by reasserting the power Magazine, 28, 121-137. CUNNINGHAM, E F. 1990. James David Forbes: Pioneer of geographical causes over astronomical causes: 'I Scottish Geologist. Scottish Academic Press, consider the former changes of climate and the Edinburgh. quantity of ice and snow now stored up in polar DARWIN, F. & SEWARD, A. C. (eds) 1903. More letters of latitudes to have been governed chiefly by geo- Charles Danvin. 2 vols. Murray, London. graphical conditions' (Lyell 1872, p. 284). DIDEROT, D. & D'ALEMBER'r. J. (eds) 1751-1765. Encyclopdgdie, ou Dictionnaire raisonng des sciences, des arts et des mdtiers. Briasson, Paris, Conclusion vol. 8. 280-286. During Lyell's lifetime many of the major FLEMING, J. R. 1990. Meteorology in America, 1800-1870. Johns Hopkins University Press, mechanisms of climatic change were proposed, if Baltimore. not yet fully explored: changes in solar output, 1997. Meteorological observing systems before changes in the Earth's orbital geometry, changes in 1870 in England, France, Germany, Russia, and the terrestrial geography, and changes in atmospheric USA: a review and comparison. World transparency and composition. New climate theo- Meteorological Organization Bulletin 46, 249-258. ries were introduced and new work was done on -- 1998. Historical Perspectives on Climate Change. heat budgets, spectroscopy and the rising carbon Oxford University Press, Oxford & New York. dioxide content of the atmosphere. Although older FOURIER, J. 1824. Remarques grnrrales sur les theories of human agency were disproved, new temprratures du globe terrestre et des espaces plan&aires. Annales de Chimie et de Physique, ser. ideas about industrial impacts were beginning to 2, 27, 136-167. circulate. Through such tempestuous theoretical HERSCHEL. J. F. W. Papers. Royal Society Library, waters, Lyell kept a steady course, providing his London. readers with reasoned arguments why they should IMBRIE, J. 8,: IMBRIE, K. P. 1979. Ice Ages: Solving the keep faith in actualist-that is mid-nineteenth Mystery. Enslow, Short Hills, NJ. century actualist-geological processes. Lyell's IPCC 1995. Intergovernmental Panel on Climate Change, ideas on climatic change can be understood only in Geneva. Switzerland. http://www.ipcc.ch/. the context of the times; but we can understand the IRONS, J. C. 1896. Autobiographical Sketch of darnes Croll times themselves better by studying Lyell's negoti- with Memoir of His Life and Work. E. Stanford, London. ated responses to new theories of climatic change. LYELL, C. 1830-1832. Principles of Geology. 1st edn. If Lyell eschewed the deplorable speculation of Murray, London. the geological system builders who had preceded 1853. Principles of Geology. 9th edn. Murray, him, he also engaged, quite systematically, in London. disciplined speculation of his own on climate 1866-1868. Principles of Geology. 10th edn. matters. If, as he pointed out, we are prejudiced by Murray, London. our limited conception of geological time and our 1872. Principles of Geology. llth edn. Murray, surficial habitats, so too are we immersed in the London. climate itself, heavily dependent on imagination Papers. University of Edinburgh Library, Edinburgh. and the assistance of others if we are ever to RAMSAY, M. 1909-1910. Orogenesis und klima. Ofi,ersigt envision a system as vast as the Earth's climate and af Finska Vetenskaps-Societetens F6rhandlingar, to apprehend its secular changes. Lyell followed the 53, 1-48. speculations of others, up to a point, but he RUDWlCK. M. 1990. Introduction. h~: LYELL,C. Principles tempered his judgements with solid evidence of Geology. University of Chicago Press, Chicago, gathered from the record of the rocks. If being vii-lviiii. thoroughly Lyellian meant being scientific in such TYNDALL,J. 1861. On the absorption and radiation of heat matters, then it also meant being cautious and by gases and vapours, and on the physical judgemental. If he was speculative on some issues, connexion of radiation, absorption, and conduction. Philosophical Magazine, set. 4, 22, 169-194, he was very very certain about many others. These 273-285. were not bad attributes to possess on a topic as WILSON, L. G. 1972. Charles Lvell. The Years to 1841: nebulous as climatic change. Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

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The Revolution in Geology. Yale University Press, Bearings upon the Antiquity of Man, with an New Haven. appendix on The Probable Cause of Glaciation bv WRIGHT, G. F. ! 889. The Ice Age in North America and its Warren Upham. D. Appleton, New York.