Thoreau's View of Science*
One of the crucial intellectual events of the Nineteenth Century was the rapid expansion of scientific knowledge. The accompanying problems of man's view of himself in relation to the new universe occupied scientists, clergymen, and laypeople alike, and the positions then defined remain with us in many ways today. In that century, perhaps few stances towards science are as interesting as that of the transcendentalist, which began in scientific radicalism and ended totally opposed to scientific aims, methods, and assumptions. Among the Transcendentalists, the most seriously concerned with the question of science, because the most dedicated to a life in nature, was Thoreau.
Thoreau's attitudes towards nature cannot be wholly considered apart from his views on science, since he constantly illuminated his approach to nature by contrasts and parallels to science; hence, full-scale studies of Thoreau invariably consider these views and attitudes. In his biography of 1873 William Ellery Channing used the phrase "poet-naturalist" to resolve the dichotomy in Thoreau's work between subjective interpretation and objective reporting. Yet the dichotomy persisted. Naturalists continued to be appalled at the inaccuracy of the reporting, humanists to be exasperated at its inclusion at all.
At the present time there seem to be three readings of Thoreau's science, the ecological, humanist, and symbolist. A minority of critics finds him a true scientist ahead of his time, an ecologist before ecology existed.  But this reading ignores a pronounced anti-scientific bias in Thoreau's writings which becomes stronger as he becomes more obviously scientific. This puzzle--that his late journals are at once more scientific in content and more opposed to science in comment--has been solved by no interpretation.
The humanist view understands Thoreau as unalterably opposed to science but lapsing into it through loss of inspiration.  It ignores the enigma's converse, the many cordial remarks about science in the earlier writings. The third and most widely held view of Thoreau, the symbolist, believes that he was always a poet, never a scientist by lapse or choice. The late journals are unutilized storehouses which testify to the continuity of Thoreau's attitudes throughout life. 
I would like to suggest that Thoreau has a far more complex attitude towards science, and to suggest its origins. His basic difficulty may be summarized thus: he believed in 1842 that he could be a Transcendentalist and a scientist simultaneously. In "The Natural History of Massachusetts" (1842), his first nature essay, he was convinced that science must lead to transcendental ends, and he accepted it enthusiastically. The untenability of this position gradually became clear to him in two ways, and this gradual clarification is the history of his scientific thought. First, his approach failed. He could not prove what he had intended to prove with the facts he had gathered. Second, he learned that the assumptions of his approach were not accepted by scientists.
Thoreau, as everyone knows, became interested in nature because of Emerson, but it is not noted often enough that Emerson brought Thoreau to nature through scientific writing. Writing to Margaret Fuller on April 10, 1842, Emerson notes:
Why did Emerson choose this way to interest Thoreau in the Concord landscape? First, Emerson is introducing Thoreau to method as well as subject. Second, Emerson's own excitement about nature had been aroused by science.
Emerson, attempting to save religion from dogmatism, institutionalism, and error, tested everything for its expediency in furthering his urgent aim. Though rejecting revealed religion, with its source in the Bible and support in the churches, he had felt no need to abandon natural religion. He needed a substitute for the Bible, and nature had long been so used. But conventional natural theology used nature to support revealed religion by stressing the limitations of human life and knowledge. Swedenborg, however, introduced into New England by Sampson Reed, suggested a more optimistic interpretation of nature. He said that the mind was destined to expand to divinity through increased knowledge of nature. Reed's work stressed science heavily."  But his assertions remained unfelt by Emerson until his European trip in the summer of 1833.
The moment of awakening came in the Jardin des Plantes in Paris, where Emerson looked, not on the face of nature wild, but on nature arranged and methodized. The vast scope of the collection told him that "the universe is a more amazing puzzle than ever"; the orderly display told him at the same time of the capacity of the human mind to encompass and understand this universe; and his own deep emotion in the presence of this combination of mind and matter assured him that science was the key to the religion of the futures.  This vision inspired, the following winter, a number of lectures on science, for which Emerson read widely and enthusiastically. He saw the science of the Jardin as a dictionary of the language of nature. "Nature is a language and every new fact we learn is a new word.... I wish to learn this language, not that I may know a new grammar, but that I may read the great book which is written in that tongue."  He wanted science to advance at full speed, for every discovery teaches Divinity and cements our connection to God. He had no conventional fears of scientific impiety. No fact could shake his religious certainty, for his conception of Deity was vaster than fact. "I am not impressed by solitary marks of designing wisdom; I am thrilled by the choral harmony of the whole. Design! It is all design. It is all beauty. It is all astonishment." 
In his fight against established religion Emerson found science an ally and a key to understanding the universe in the way he was predisposed to understand it. Here were the mind and the universe merging. Here were progress and optimism. He was better prepared than some scientists of his own day to accept a number of discoveries, such as the great age of the earth, because, being completely non-materialistic, he found nothing disturbing in the ability of secondary causes to explain material effects. How else, he might ask, were material effects to be caused? But what animates the causes? 'Life,' or 'Spirit.' This non-materialism, which led him to equate 'life' with 'spirit,' blinded him entirely to the possibility that secondary causes might ever be extended to account for the existence of life itself. Thus secure in his definition of ends, he cautioned scientists against forgetting ends in their natural delight over means." 
Emerson turned Thoreau to nature study, then, not through his Nature, but through scientific documents. It seems fair to surmise that he was trying to move Thoreau in the same way and by the same means as he had been moved. "I say I will listen to this invitation. I will be a naturalist,"he had written nine years before.  Now he was passing this invitation on to Thoreau.
Thoreau reviewed the surveys in an essay entitled "The Natural History of Massachusetts," which shows his happy acceptance both of nature and science. The surveys are welcomed to the select company of books which "restore the tone of the system," contrasted to the irrelevant "din of literature, religion, and philosophy." The scientific method which they proceed from is "admirable training . . . for the more active warfare of life." Linnaeus is compared to Napoleon. Nature repays the most exacting scrutiny; she "invites us to lay our eye level with the smallest leaf, and take an insect view of its plain."  The only criticism he offers is of the unavoidable incompleteness of the surveys. "These volumes deal much in measurements and minute descriptions, not interesting to the general reader. . . . But the ground was comparatively unbroken; and we will not complain of the pioneer, if he raises no flowers with his first crop" (p. 130). The surveys are inadequate because they are first efforts. But they are ground-breaking, full of healthy promise. There is no distrust in Thoreau's welcome.
Thoreau was not, of course, simply a copy of Emerson, and he worked into his welcome of science his own ideas. As religious as Emerson, he was as anxious to define man's proper relationship to a Power assumed to have created the universe and still actively sustaining it. As transcendental as Emerson, he believed that this Power could be directly known by man through intuitions arising from his own internal divinity. These intuitions are supported by the evidences of nature around him, which, as it was created by the Mind he shares, can be perceived and understood by him. But, more Calvinist than Emerson, Thoreau had a strong sense of man estranged from God. So, when he accepted the scientific approach, he turned the scientific life into a holy life of great effort and infinite challenge. In Thoreau's relationship with nature we do not find Emerson's pacific certainty. To study nature becomes the program of an action which achieves the reconciliation of man and God. The naturalist lives a saintly life because he must obey the laws he learns to know them, and these laws explain him and his place in the universe, being spiritual as well as material laws. It is quite scientific, then, to plant beans for the sake of parables; through beans spiritual truths are revealed.
Thoreau's word for this program of nature study, which was identical with the quest for personal salvation, is anticipation,' and we may find the seeds of anticipation in various semi-scientific works which he read in his formative years. There is, first of all, Emerson's early lecture, "The Uses of Natural History," delivered during the winter of 1833-1834. The fourth in an ascending quintet of uses is the effect of nature study on the student--the production of quickness, reverence, love for truth, bravery. These qualities develop because the naturalist "commands nature by obeying her."  The highest use is the extension of man's self-knowledge, by which Emerson means knowledge of ones "true place in the system of being." Though man is a spiritual creature, he must learn his spiritual laws in and through a material world, because that world is the only language (p. 24).
A second influental work is William Howitt's Book of the Seasons,3, or The Calendar of Nature.  Thoreau reviewed this work in his youth, and referred to it sporadically throughout his life.  Its format, observations and meditations arranged by months and accompanied by tables of migrating birds, blooming flowers, budding trees, and emerging insects, was the prototype for his own late project, an unrealized calendar. Howitt held that delight in nature is useless if not instructed; Using Linnaeus as his authority,urged readers to make tables like his, watching for the dates of bloom and decay. For, he says, "we see trees open their buds and expand their leaves, from whence we conclude that spring approaches; and experience supports us in the conclusion; but nobody has, as yet, been able to show us what trees Providence has intended shall be our calendar, so that we might know on what day the countryman ought to sow his corn." Noting when leaves fall will teach us" to guess at the approach of winter." Indeed, Howitt concludes, "the hints of Linnaeus constitute a universal rule for the whole world" (p. 101) Howitt is thinking of strictly practical uses for his tables, but his language is virtually identical to Thoreau's; one needs only to make a correspondence between material and spiritual corn.
A third scientific source (Howitt is not science, but he rests his case on Linnaeus) is Thoreau's natural history text, Smellie's Philosophy of Natural History.  This book explains in its chapter on instinct that some animal behavior proceeds from powers similar to man's--reasoning, judgment, volition--but "the prudence and anticipation of remote consequences so often exhibited by animals can only come from instinct" (p. 109). In "The Natural History of Massachusetts," Thoreau sees the complete scientist as a person who has reacquired instincts. "The true man of science will know nature better by his finer organization; he will smell, taste, see, hear, feel better than other men.... The most scientific will still be the healthiest and friendliest man, and possess a more perfect Indian wisdom" (V, 131). Thoreau's writings show that by Indian wisdom he means instinct. "Often, when an Indian says, 'I don't know,' in regard to the route he is to take, he does not mean what a white man would by these words, for his Indian instinct may tell him still as much as the most confident white man knows" (III, 203).
The laws of the universe are a great rhythm, to which man at his most fulfilled moments marches. If a sense for this universal rhythm is implanted in the creature, he always moves with the music. Such a sense is instinct, possessed by animals and possibly by Indians. In civilized men, rhythm is not implanted, and there is substituted a capacity to learn the music. This substitution is man's, at least the white mans, curse and challenge; it is the sign that he has been expelled from the garden: of Eden, but in true Miltonic fashion it is the sign that there is a peculiarly human, and therefore superior, way to regain it. The way back is through learning, which ultimately approaches instinct. When man has learned the music so thoroughly that he can anticipate it, when he knows what comes next, he will be able to keep time.
Thoreau devoted the rest of his life to learning nature well enough to "anticipate" her. Natures cyclical organization assured him that anticipation was possible, for in repetition lay the hope of learning, correcting, refining, and profiting from past error. Certain patterns obtruded immediately: the alternation of day and night, the succession of the seasons. These broad patterns could be quickly learned so that man might keep his life in some rough harmony, such that his ignorance did not destroy him. The next step was to sharpen perception and make out finer patterns, and more precise regularities. Spring certainly follows winter, but when? This question subdivides--where, on what day, does the first crocus spring? When do the geese fly over Concord?
The sequence of Thoreau's work, from the breezy acceptance of challenge in "The Natural History of Massachusetts" to the bird lists of the late journals, can be seen as the attempt to find nature's laws in increasing detail. The so-called scientific entries of the late journals invariably organize themselves around the all-important question of time and are permeated by the repeated refrain, "How long?"
These notes, extending over years, were the raw material for his calendar, which is thus different from Thoreau's other works only in the detailed nature of the material it assembles to anticipate nature. It contains that same assertion of human possibility and responsibility which illuminates Walden. Nature invites us and will not disappoint our expectations. Nature can be anticipated, and therefore man has his work to do.
But, reading the late journals and seeing what Thoreau finally did with the material he had collected for the calendar, one senses that Thoreau approached, if he did not accept, the realization that the task, as he had defined it, was impossible. Partly, he needed instruments and manuals to see what could be seen and know what he saw; partly, too, nature was simply not as regular as he had assumed. The arrangements of his calendars were continually being upset by a continuously baffling and erratic factor--the weather. Surveyor of the seasons, Thoreau occupied himself with rendering the boundary line in time between spring and winter with absolute precision, learning day by day the tiny signs that told time,  only to find that precision was impossible because the boundary line was unstable. "Though you walk every day, you do not foresee what kind of walking you will have the next day. Skating, crusted snow, slosh, etc., are wont to take you by surprise."  Cold winters, long winters, winter thaws, spring frosts, great snows, floods, draughts, heat spells--the calendar seemed at times less a chronicle of repetition than of aberrations.
There are two interpretations for this weather. One may concede that nature is irregular, repeating itself only roughly, more an average of probabilities-than an exact system. Such an interpretation incorporates chance into the system, equivalent for Thoreau to taking God out of it, so closely did he, following Emerson, identify God with law. Thus this interpretation is impossible for him.
Second, one may insist that nature is perfectly regular but decide that one's measuring instruments--for the Transcendentalist necessarily the almost unaided senses sharpened by self-discipline and confined to the term of a single life--are not properly designed to record the precision. "It takes us many years to find out that Nature repeats herself annually. But how perfectly regular and calculable all her phenomena must appear to a mind that has observed her for a thousand years!"  But the pattern that can be discerned only with microscope and telescope is not a human pattern, and the mind that has observed for a thousand years is not a human mind. Now the whole point of anticipation was its use for man. If the laws of the universe exist in a way not knowable or perceptible by the individual, not only does the study of nature seem pointless but the whole man-centered cosmos comes into question. Thoreau believed that the world was God's text-book; its source was divine, its intention human. The universe in its vast regularity may still be divine, but it has lost its human purpose. God and the creation are taken away from man, opening the very gap anticipation was meant to close. God's intelligence and human intelligence are sharply distinguished, while the Transcendentalist based his faith on a human participation in the divine mind.
The problem of the irregular universe does not arise in Walden because the correspondence of the protagonist's life to the seasons is on the largest and most general levels only. The hero must anticipate the limit of winter, believe in the return of spring, know when to plant beans and when to sound the pond. From the vantage-point of the late journals, Walden is but the roughest blocking out. By 1859, though, it would begin to seem that Walden's roughness was the limit of accuracy. The hero of an 1859 Walden would have no use for all the knowledge he had acquired in the intervening years.
In the essays prepared for publication immediately before his death, Thoreau seems to have been concerned to find another use for his storehouses. Accepting, at long last, that God would not make him a partner, he contents himself with learning nature for pleasure. The end of such essays as "Autumnal Tints" and "Wild Apples" is simply the increased enjoyment of the rigorous observer. "But of much more importance than a knowledge of the names and distinctions of color is the joy and exhilaration which these colored leaves excite."  Fine discrimination and detailed knowledge is to be cultivated as an aid to appreciation; the transcendental position towards nature must be that of the informed amateur. This is a failure, to be sure, but the failure is not in Thoreau. It is in the program, which has been followed as far as it can reasonably be followed, and which issues in a kind of conservatism towards science far from the radical enthusiasm which motivated it.
As Thoreau was pursuing his way through this difficulty, science too had come to recognize that nature had a temporal as well as a spatial existence, and accepted a non-human scale for that existence. But the intelligibility or usefulness of the universe was not thereby negated, because for science the unit of knowability was not the single, unaided perceiver. Thus the internal logic of science went one way while Thoreau went a different way. Following, then, his program of anticipation with great fidelity, Thoreau found that he had set himself an impossible task. At the same time he was also becoming aware of another sort of disturbing fact. The ends he was seeking in nature were increasingly rejected as legitimate scientific ends. Science was changing, and its happy ministration to transcendental idealism was proving to have been a vision. What had seemed inevitable to Emerson in 1833 seemed ridiculous in 1853, as Thoreau defensively acknowledged in his journals. While in 1833, when Emerson had discovered science, conservative scientists were still fretting about the Flood, they were in 1853 bracing themselves for Darwin. These developments created repercussions and difficulties not merely in the relations between science and other disciplines and philosophies, but within science itself. Historians of nineteenth-century science have shown to what great extent scientists were troubled, confused, and divided, and to what great extent general philosophical and religious attitudes colored scientific controversy on all professional levels. 
There are perhaps four separable conflicts, none of which oppose religious to nonreligious minds, as they derive rather from different notions of deity and of the legitimate role of science in explaining deity than from degrees of piety. All sides used religious arguments.
One argument centered on the question of how God made and sustained the universe. Did he intervene in its functioning? Lyell's Principles of Geology was dismaying, to be sure, because it contradicted the Bible, but more disturbing was the fact that it made God's constant supervision of the earth unnecessary. Lyell was doing for the earth what Newton had done for the cosmos--suggesting that God worked by immutable and uniform laws which ran the universe without him, for which he had been directly necessary only once, and which he himself could no longer abrogate. What Lyell suggested for the planet, Darwin was soon to posit for the life on it.
The notion that earth and its life were created and altered by specific, disconnected fiats, and sustained by constant overseeing, died very hard. But the opponents of the notion appealed to religious sentiment as vigorously as its adherents. In his Vestiges of Creation, Robert Chambers insisted "when all is seen to be the result of law, the idea of an Almighty Author becomes irresistible, for the creation of a law for an endless series of phenomena--an act of intelligence above all else that we can conceive--could have no other imaginable source."  Just this notion of the whole world working by uniform law had excited Emerson, for to him the fact that anything worked at all was miracle enough. Thoreau agreed. "Though I do not believe that a plant will spring up where no seed has been, I have great faith in a seed,--a,to me, equally mysterious origin for it." 
In this argument Emerson and Thoreau agreed with the more radical scientists of their own time, opposed, for example, to Agassiz, who wrote in his zoology text, "There is nothing like parental descent connecting [the different species]. . . . The link by which they are connected is of a higher and immaterial nature, and their connection is to be sought in the view of the Creator himself."  But in another argument Emerson and Agassiz were firmly aligned. This was the question of whether discussions of first causes are appropriate at all in science. Emerson certainly agreed with the train of thought which led Agassiz up from nature to God. Discussion of secondary causes without reference to the first cause was impious or meaningless. But others felt that to presume to speak with authority for God's intentions was more impious and meaningless still. "The geologist sadly mistakes both the object of his science and the limits of his understanding, who thinks it his business to explain the means employed by INFINITE WISDOM for establishing the laws which now govern the world."  Most of those who believed in uniform law also believed that first causes should be kept out of science; the Transcendentalists were in the less usual position of insisting both on uniform law and on constant reference to first cause.
A second pair of questions revolved around the nature of man. What is his place on earth? One view enjoined man to be humble; the other encouraged his pride. "In view of all these facts," Emerson proclaimed, "I conclude that other creatures reside in particular places ... but the residence of man is the world. It was given to him to possess it."  We have already seen that Emerson accepted science largely because it answered his vast conceptions of man and God. To him it implied a rebellion against conservative pessimism. "But I think the paramount source of the religious revolution was Modern Science.... Astronomy taught us our insignificance in Nature; showed that our sacred as our profane history had been written in gross ignorance of the laws, which were far grander than we knew and compelled a certain extension and uplifting of our views of the Deity and his Providence. This correction of our superstitions was confirmed by the new science of Geology, and the whole train of discoveries in every department." 
But that conservative pessimism decried by Emerson had been and continued to be supported by science also. Paley, who conventionalized the application of science to religious argument, used science to show the insufficiency of life on earth and imply the need for Revelation. Pope's Essay on Man brought scientific knowledge to the support of a view of man as a poor, circumscribed creature whose life was "good" only in terms of a vast divine plan beyond his powers to comprehend. This view is echoed into the nineteenth century in such standard works as Smellie's Natural History: "Let man therefore be contented with the powers and the sphere of action assigned him. There is an exact adaptation of his powers, capacities, and desires, both bodily and intellectual, to the scene in which he is destined to move. . . . Let him fill up his rank here with dignity, and consider every partial evil as a cause, or an effect, of general ultimate good" (p. 311).
The second question, about man's nature came to be epitomized, for Thoreau, in the question of the relation of the scientist to the material he was discovering and the laws he was deriving. The question at issue is in a sense the question of the set of concepts used to understand nature. Pre-Newtonian science used for its concepts the Aristotelian qualities, which described attributes perceptible to the senses, qualities which were as much responses in the perceiver as inherent characteristics of the object. Thus the perceiver is central in this set of measuring terms; he is the instrument specifically designed to register the nature of objects. It is easy enough then to hold that the purpose of the perceived object is exactly the perception of it by man, and the question of whether man or nature is then studied has no meaning.
Newton, besides creating a universe that required God only once, explained it by a set of concepts which shut men's normal perceptions away from an operational understanding of the world, and made their observations seem irrelevant to the cosmic organization.  The distinction between mind and matter, "the strongest distinction of which we have an idea,"  and the preoccupation of many post-Newtonian philosophers with epistemology, can be understood at least partly as developments from these explanations which made the human view of the world seem literally "superficial." Now Emerson had attempted to solve the problem of epistemology by a kind of platonic intuitive idealism. He had also attempted to negate the dualism by insisting that what man knows through his senses is also real. The world is both as men intuit it to be and as it appears to them. In short, Emerson had bridged the Cartesian dualism by returning to a pre-Newtonian vocabulary, thus insisting that nature is designed for human perception and action, and that its only meaningful description is in terms of human perception of it and responses to it. At the heart of Emerson's system of understanding nature is the perceiver. 
This perceiver turned active is the heroic scientist in Thoreau's system, and it was for the scientist himself, as Thoreau understood it, that the whole set of observations had, ultimately, meaning. "Will you be a reader, a student merely, or a seer?"  Unwilling even to use spy glasses, he held that "the naked eye may easily see farther than the armed"  He held these views because to him the scientist was not engaged in a professional activity, but a symbolic one in which he stood for all men. But science was coming more and more to eliminate the personality and the capacities of the investigator from the investigation, to objectify observation, refine it with instruments, and ultimately to make it as little as possible dependent on the perceiving sense of the scientist. The self-centeredness of Thoreau's investigation, the question of what the scientist personally underwent in the course of his investigations--in short, the whole philosophical point of Thoreau's quest--was deliberately excised. "I think that the man of science makes this mistake, and the mass of mankind along with him: that you should coolly give your chief attention to the phenomenon which excites you as something independent of you, and not as it is related to you."  But mistaken science flourished while "anticipation" floundered.
For Thoreau the meaning of every fact was the purpose it served in human education, a purpose not subjective in the sense of idiosyncratic, but decreed by God and accessible to all men in nature--subjective, however, in requiring a personal participation to be known. A man cannot know the significance of a fact if he does not allow his response to the fact to enter into his observations. In Thoreau's study, the searcher stood for all searchers, and in this sense was impersonal; but he was also necessarily subjective because the meaning of the fact became known subjectively. The meaning of every fact in the world is thus "human." The fact means what it is felt to mean by human intelligence when it is seen by human perception. The aim of science, as Thoreau saw it developing, was to study sound divorced from the ear which heard it. But to him the sound was only meaningful to the hearing ear, which must therefore be included in a description of the sound.
What is the relationship between a bird and the ear that appreciates its melody, to whom, perchance, it is more charming and significant than to any else? Certainly they are intimately related, and one was made for the other. It is a natural fact. If I were to discover that a certain kind of stone by the pond-shore was affected, say partially disintegrated, by a particular natural sound, as a bird or insect, I see that one could not be completely described without describing the other. I am that rock by the pond-side. 
That there are on the one hand sounds and on the other ears capable of hearing them is Thoreau's proof that the entire world has been constructed with man at its center.
By 1853, a decade after he had so willingly undertaken his Emersonian burden, Thoreau had become aware of the split between himself and science, and it bothered him so much that when he received a questionnaire from the American Association for the Advancement of Science he reacted with a quite uncharacteristic peevishness.
The uneasiness betrayed in this passage increased with years. Thoreau's own belief in the intentional shape of the universe, though too firm to be shaken, received shocks within his own symbolic world: the "vast, and dread and inhuman" chaos on Mt. Ktaadn, where "was clearly felt the, presence of a force not bound to be kind to man,"  for example, and the savage ocean so painfully dealt with in Cape Cod. But he clung to his faith all the more fiercely for the difficulties it gave him.
He could only insist that science was missing the point, and he did, but here he ran into the trouble that although he could call science "wrong" he could not call it "false." Scientific facts could not be dismissed like "facts" in the newspapers or the post office, because they were the facts with which he himself worked. To dismiss science as man-made, a shallow manipulation of artificial nomenclature, became a common attack in the late journals. "Whatever aid is to be derived from the use of a scientific term, we can never begin to see anything as it is so long as we remember the scientific term which always our ignorance has imposed on it."  But his dilemma is well shown by the fact that these passages occur in the midst of observations in which he himself was using the scientific terminology he deplored. Elsewhere he admitted this dependence that he always covertly acknowledged. "With the knowledge of the name comes a distincter recognition and knowledge of the thing. . . . My knowledge was cramped and confined before, and grew rusty because not used,--for it could not be used. My knowledge now becomes communicable and grows by communication."  That he ever wrote "The Succession of Forest Trees," a late (1860) and deliberately scientific essay, betrays the same ambivalence.
In general, by the end of his life, Thoreau no longer saw scientists as pioneers, but as members of the reactionary fraternity along with, for example, missionaries. In the Maine Woods he was delighted at the inexplicable (as he hoped) mystery of the will o' the wisp, clinging to it as something which, by defying scientific explanation, proved the religious character of the universe (III, 200-201). This is a complete reversal of the position taken in "The Natural History of Massachusetts." In his late journals he frequently compared the early naturalists, quaint, credulous, unable to tell fact from fable, but with a sense of wonder and miracle fully playing over the world--he compared these legendary figures with the modern scientist, to the latter's disadvantage. "So far as natural history is concerned, you often have your choice between uninteresting truth and interesting falsehood."  This he said in 1860; in 1842 he had said that to know is to know what is good.
The growth of the number of strictures against science in the late journals records his realization that science was not what he had taken it to be, and is a separate development from the private collapse of his "anticipation" enterprise. There is no evidence that he brought these two developments together in his own mind, and yet together they pointed to the same thing--the irrelevance of man in the universe. It was inconceivable that Thoreau could ever come to accept the position against which his whole life had been aimed. He turned on those who were apparently able to accept it, for if it was horrible to imagine a world in which men were irrelevant, it was perhaps almost as horrible to watch the spread of a type who thought they were irrelevant; for we always lead, do we not, the life we imagine we are leading? Yet Thoreau could hardly, with his deep devotion to truth, have urged his world-view on others as a comforting or sustaining illusion. And so he turned against his early pioneers, dissociated himself from their efforts even as he acknowledged that what they are saying is true and went back to the old naturalists, to whom "gorgons and flying dragons were not incredible." 
1 See, e.g., Raymond Adams, "Thoreau's Science," Scientific Monthly, LX (1945) 379-382; Charles Metzger, "Thoreau on Science," Annals of Science, XII (1956), 206-211; Leo Stoller, After Walden (Stanford, 1957) ; Kathryn Whitford, "Thoreau and the Woodlots of Concord," New England Quarterly, XXIII (1950), 291-306; Kathryn Whitford and Peter Whitford, "Thoreau; Pioneer Ecologist and Conservationist," Scientific Monthly, LYXIII (1951), 291-296. (In the 1990s this view has become predominant, as more up-to-date bibliographies will make clear. But "ecology" itself now covers a range of attitudes toward science.")
2 See, e.g., Brooks Atkinson, Henry Thoreau, the Cosmic Yankee (New York, 1927); Henry Seidel Canby, Thoreau (Boston, 1939); Joseph Wood Krutch, Thoreau (New York, 1948); Mark Van Doren, Thoreau, a Critical Study (Boston, 1916).
3 The best example is Sherman Paul, The Shores of America (Urbana, 1958).
4 Ralph Waldo Emerson, Letters, edited by Ralph L. Rusk (New York, 1939), III, 47.
5 See Sampson Reed, Observations on the Growth of the Mind (Boston, 1826), 42-59; also his "Oration on Genius" in Perry Miller, ed., The Transcendentalists (Cambridge, Mass., 1950), 51-53.
6 Ralph Waldo Emerson, Journals, ed. E. W. Emerson and W. E. Forbes, (Boston, 1909-1914), III, 161-164. Also H. H. Clark, "Emerson and Science," Philological Quarterly, X (1931), 225-260.
7 "The Uses of Natural History," in The Early Lectures of Ralph Waldo Emerson, ed. Stephen Whicher and George Spiller (Cambridge, Mass., 1959), 24.
8 "On the Relation of Man to the Globe," Early Lectures, op. cit., 49.
9 "The Naturalist," Early Lectures, 29.
10 Journals, III, 164.
11 "The Writings of Henry David, Thoreau (Boston, 1906) vol. V, 105, 107. All references to Thoreau unless otherwise identified are to this edition, the Walden, which includes the Journals.
12 Early Lectures, 25, 20.
13 London and Philadelphia, 1831.
14 See Wendell Glick, "Three New Early Mss. by Thoreau," Huntington Library Quarterly, XV (1951), 59-71.
15 Revised by John Ware (Boston, 1824).
16 Journals, X, 379-395 passim. The volume number of the journals is given, not the number of the volume in the Writings.
17 For an example, see Journals, XIII, 218-229, where March has a daily timetable.
18 Journals, XIII, 108.
19 Journals, XIII, 279.
20 "Autumnal Tints," V, 274.
21 See, e.g., Charles Gillispie, Genesis and Geology (Cambridge, Mass., 1951); Bentley Glass, ed., Forerunners of Darwin (Baltimore, 1959).
22 (London, 1844), 158.
23 "The Succession of Forest Trees," V, 203.
24 L. Agassiz and A. A. Gould, Principles of Zoology (Boston, 1848), 417-418.
25 John Playfair, Illustrations of the Huttonian Theory of the Earth (Edinburgh, 1802), 132. Emerson read this for his early lectures. (Letters, 1, 403.)
26 "On the Relation of Man to the Globe," Early Lectures, 49.
27 "Historic Notes of Life and Letters in New England," The Transcendentalists 499.
28 See E. A. Burtt, The Metaphysical Foundations of Modem Science (New York, 1925; Anchor, 1954), 26-27, 89-90, 236-239.
29 Emerson, "The Uses of Natural History," Early Lectures, 24.
30 Sherman Paul, Emerson's Angle of Vision (Cambridge, Mass.), 1952.
31 Walden, II, 122.
32 Journals, IV, 471.
33 Journals, X, 164-165.
34 Journals, IX, 274-275.
35 Journals, V., 4-5.
36 Maine Woods, III, 77-78.
37 Journals, XIII, 141.
38 Journals, XI, 137.
39 Journals, XIII, 181.
40 Journals XIII, 180.
*Slightly revised from original publication in the Journal of the History of Ideas, 26 (1963): 221-34.