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- Agriculture is a trade with the purpose... to produce profit or to gain money. The higher this benefit in the long run, the more complete this purpose is fulfilled.
- Thaer (1810) cited in: Martin Frielinghaus and Claus Dalchow. "Thaer 200 years at Möglin (Germany)." in documentation.ird.fr. (2007): 259-267.
- Opening sentence of Thaer's four-volume Grundsatze der rationellen Landwirthschaft (Principles of Efficient Agriculture, 1809-1812).
- The proprietor should always direct his attention to obtain from his land a gradual increase of produce, or to augment its value continually. The farmer only desires the greatest profit during the continuance of his lease, without caring for the value of the land afterwards. "Whilst the proprietor can content himself with a trifling produce during a few years, in order to attain greater and more durable profit subsequently, the tenant must, on the contrary, endeavour to obtain the greatest produce, even though its amount should be diminished during the latter years of his lease; because the proprietor who wishes to farm on the best system, finds at the same time both pleasure and profit in laying out on his property as much capital as he can spare, whilst the tenant, on the contrary, withdraws as much of his pecuniary resources as possible, to employ it in other ways, or to place it at interest. The improvement of the land constitutes the pleasure of the proprietor, while the mere occupying farmer only thinks of augmenting his income. Thus the longer the lease may be, the more do the interests of the landlord and tenant become identified; the shorter the term, the more conflicting are those interests. With a lease of 24 years, a tenant ought, at least during the first two-thirds of its duration, to follow out the views of the proprietor. But the time will come when he will act on different principles, and endeavour to extract from the land a return in proportion to his outlay at the commencement.
To this must be added, that a tenant cannot have the means of laying out so much on the land as the proprietor, even if he wished to do so. The latter must pay the rent, whilst a proprietor anxious to improve can economize something from the net produce to expend on his property. The first may be compared to a merchant who trades on borrowed money; the second to one who speculates with his own funds. The former must first provide for his rent, the latter need only think of extending his speculations.
- The true yield of business is determined less by the size of the estate than by the sum of the investment.
- Thaer cited in: Marion W. Gray (2000). Productive Men, Reproductive Women: The Agrarian Household and the Emergence of Separate Spheres During the German Enlightenment. p. 267.
My Life and Confessions, for Philippine, 1786
- My father was a cool-tempered and unaffected man. Everyone who came in contact with him knew his straightforward way of acting, his scrupulous honesty; but few, very few, of his friends knew his noble and manly heart. Indifferent to praise and fame, as well as calumny, he was ever anxious to do good in silence; and it can be said of him, without fear of contradiction, that during his whole life he could never reproach himself with having been guilty of a bad or mean action.
- My mother, as much as I can remember from my early boyhood, and from what I heard of her after her death, was of a most lively temper, and possessed of a good and noble heart, but a little inclined to sensibility; her greatest pleasure was to see everyone happy about her. She loved me dearly and spoilt me. I adored her. Alas, I lost her when only a little boy, and never shall I efface from my memory the day of her death and funeral."
- I was very sickly and weak during the first years of my infancy, and was, as much as I can remember of myself, a very whimsical boy. Sometimes I learned with enthusiasm, and often found myself in such a kind of ecstasy, that I neither could see nor hear what passed around me. In these fits of thought I forgot playthings and playfellows; I was happy only in my own musings. I always preferred the company of little girls to boys. I was not ten years old when I presented them with some poetry and little verses, the effusions of my heated imagination; some of them fell into my hands in riper years, and after reading them over, I left off poetry altogether. I loved my first private teacher very much; I even can remember him now. My second teacher was a simpleton; he could never understand me, nor enter into my feelings. My antipathy to this man grew daily greater; I could not learn of him, nor could he teach me anything. At last, when in my thirteenth year, I got rid of him, and he being encumbered with debts, I gave him my saving-box when he left. Whether I did this for pity's sake, or joy to get rid of him, I did not know.
- My father sent me, the same year, to school, but here I was not in my sphere; I hated the low and vulgar conduct of my school-fellows as much as the vulgar mode of correction of the masters. However, I selected some boys a little better educated for my daily companions, especially one of the name of Strauss, who unfortunately combined with his romantic ideas a great inclination to drink; we daily played truant, but nevertheless I applied myself in my private lessons with great eagerness and perseverance to the study of mathematics, history, &c., so that I contrived to ingratiate myself in the good opinion of my masters, who never missed me during the school hours, being always ready when called to my class. My best friend amongst the masters was a teacher of the French language, named Ferry) who professed secretly all the principles of freethinkers. He procured for me all the works of Voltaire, and other French freethinkers; and some time after, when I understood English, all the works of freethinkers of that nation. This was a pretty preparation for my confirmation, which was now at hand.
- The religious instruction I received of the Lutheran pastor Bode, preparatory to my confirmation, produced no effect upon my mind in favour of the truth of our divine religion, having studied all the works written against it with so much energy. I often insinuated to pastor Bode my doubts on religious matters, but either he did not or would not understand me; I was wavering between deism and atheism, so much so, that had it not been for the love towards my revered father, and the persuasions of Ferry, I should have avoided being present at the imposing and sacred ceremony of confirmation, which produced such an effect upon my young mind, that I prayed sincerely to God to give me faith, and had I not continued to read with Ferry and one Belzing so many blasphemous works, I should have returned to my former religious principles much sooner, as I did at a later period of my life.
- I continued for some time longer to ramble with Strauss and other school-fellows, to visit coffee-houses and billiard-rooms, but had a great antipathy to other debaucheries. The company of comedians of Mr. Seiler came just now to Celle, performing comedies and tragedies. This was a new life for me; I became acquainted with each individual of this company ; they all were fond of me; the beautiful Madame Koch gave me lessons in dancing, and I suddenly deserted all my former companions, neglecting them to such a degree, that one Mackphail, considering my conduct as an insult to the whole school, sent me a challenge, which ended in ray wounding him in the hand. My father loved me dearly, but did not much inquire into my conduct; he allowed me a great deal of money, but owing to my attachment to Ferry, whose salary was but small, I provided him with money, and having myself an extravagant taste for dress, I was often in great difficulties to pay my bills, of which my father was ignorant, till my creditors became troublesome, and my good father immediately discharged them, after giving me some kind admonition.
- I was now in my sixteenth year, and for the first time it occurred to me that, although conversant with most of the modern languages, I did not understand a word of Latin, and thought the knowledge of this language indispensable to my future prospects in life. I spoke to Rector Steffens, and got permission of my father to leave school entirely, and devote my whole time to the study of Latin. In less than twelve months I was completely master of a language which is often the torment of boys from their sixth to their twentieth years, and still remain ignorant of it. Since then I have written several pamphlets in Latin, which were admired; and in Gottingen my Discourses were generally delivered in that language. Doctor Taube, physician to the king, gave me lessons in natural history, botany, and anatomy; I bade farewell to philosophy and belles lettres, and began in earnest, and with great perseverance, to study physics; but still I was in bad odour amongst many of the learned, and it was said, when they heard of my progress, that henceforth they should not despair of making something of the most stupid of pupils.
- In my eighteenth year, my father sent me to the University of Gottingen. The first winter I did not leave the Anatomical School, and although I gave myself up to the most intense study, I willingly entered into all the gaities and amusements so much sought by German students, but avoided carefully debaucheries of any kind; they gave me the cognomen, Half Benommist, owing to my puerile look and feeble and weak voice. Unzer and Ebeling, two students in physic, took me under their powerful protection, and extricated me out of many scrapes.
- In the second year of my residence in Gottingen, I entered my name for a course of lectures on practical physics, against the advice of all my friends, but I have never regretted so doing, as there never has been, and probably never will be, a greater man at the university than Doctor Schroder, physician to the king, who gave, at that period, his celebrated lectures on practical physics. Schroder himself was astonished at the step I had taken; but when he perceived that I fully understood him, I became one of his favourite pupils; nor had I the advantage alone of receiving private lessons gratis, but he took me with him in most of his professional visits, where I had all the advantages of his great practice. Thus I caught a putrid fever which was then very prevalent; Schroeder attended me day and night, and giving up all hopes of my recovery, he observed to one of his friends, not thinking that I understood what he said, "The expansion of the sinews increases." "Then," answered I, in a quiet manner, "I shall die in four days, according to such and such a rule of Hippocrates: pray, prepare my father to receive the news of my death." However, immediately after, a sudden turn in the disorder taking place, I soon recovered; not so my memory, which I lost for a time, so that I had forgotten the names of my best friends; my nerves were so completely shaken, that I had no wish to recover. After my recovery, Professor Schroeder being himself attacked with the same fever, requested of his wife that no other physician than myself should attend him; but when he became light-headed, she called in all the physicians of Gottingen, and these gentlemen not agreeing in opinion respecting the treatment of the patient, this great and learned man fell a victim to ignorance and jealousy, April 21, 1772. I cannot think of this celebrated and good man without shedding tears of regret and gratitude.
- After his death I did not attend any more lectures, although I paid for them. Schroeder was succeeded by Ernst Gottfried Baldinger, born in Gross Vargula, near Erfurt, 1738 ; and descended in a direct line, on his mother's side, from Doctor Martin Luther. He established a dispensary for poor patients, and gave medicine gratia, on condition of his being attended by about thirty pupils. Here it was that I first began to display the knowledge I had gained from my friend, the late Doctor Schroeder; and Baldinger, not seeing me attend his lectures, naturally supposing I was lazy and dull of comprehension, exclaimed, with astonishment, "What will become of this boy?" Whereupon, considering myself insulted by the Doctor, I wished to retire; when he embraced me, and said, good-humouredly, "No, no such a clever young fellow never came under my observation." From this time I became his best friend and daily visitor; I passed whole days and weeks in his valuable and extensive library, and almost in the constant society of his amiable, highly gifted, and accomplished wife; his confidence was so great, that he left the entire direction of his dispensary to me, and even entrusted me with the care of his own family when unwell. Having given up all connexion with my former friends, the students, I selected one Leisewitz, the author of "Julius de Tarent." We sympathised in each other's feelings, and became inseparable. His amiable qualities and inoffensive wit drew around us the best society; but, to our great regret, many of them belonged to a new school of freethinkers, whose principles we endeavoured, by the assistance of the pious Madame Baldinger, to eradicate from their minds; and thus it was thnt Providence brought me over again to the firm belief of the truth of our Divine religion.
- In the mean time I paid the strictest attention to my profession, and was so completely successful, that there was no patient of any consequence in Gottingen that I was not called in to; but as I was not allowed to make up prescriptions, not having taken my degree, and in order to avoid a heavy penalty, I was accompanied in my professional visits by Doctor Tolle, a man who knew the lectures of Schroder by heart, but did not understand them. I dictated to him what to prescribe, he took the fee, and was content. I had nothing but the honour, and plenty of good dinners. At last I took my degree as Doctor of Medicine, and resigned my patients to the care of Dr. Strohmeyer, which was the means of introducing him into practice. I left Gottingen full of honour, with tears in my eyes, at leaving behind me so many dear friends. Puffed up with pride, I arrived in Celle, but was received with coldness and pity. This was too much for mc; I could not brook the insult; but said to myself, "How can I expect to be otherwise received, when I consider my former conduct, and look back on the heedless manner in which I passed my boyish years?" My consolation was, that "I should be soon as happy here as I was in Gottingen" in the choice of my friends.
- The physicians in Celle were fifteen years behind in their practice; they had heard of a new style of practice, but regarded it as a mere chimera. When I ventured to say a word or two, they did not understand me: when I appealed to some great authority, they were ignorant of it: when I spoke from my own practical experience, they looked at me, from head to foot, and said sneeringly, "Well, well; experience will come in time." But when by chance I ventured to make some proposal, they turned round, and wondered where they should find room enough in the churchyards to bury my patients. The great applause with which my Dissertations had been received in all the learned journals, even in England as well as in France, gave me courage, hoping that this circumstance would make some impression on the mind of the public; but it was generally thought I had ill employed my time, and knew little or nothing. Being obliged to frequent society, I was so disgusted with the general tone and the topics of their conversation, that I was almost in despair; at last, some young ladies treated me with more attention.
- I began to reconcile myself to my forlorn condition, but still I was not what I wished to be: the worst of all was, I had no friend; not a human being that understood me. I wrote daily to my friend Leisewitz; he resided in Hanover, and was just as unhappy as myself, except that he had some friends, and plenty of money. In this respect I was differently situated, and although in want of money to buy books, I was determined not to be any expense to my father. Some watches, snuff-boxes, and rings, presents I had received in Gottingen, soon found their way to the hands of Jews at half price. I was even, against my will, driven to the necessity of accepting small fees from mechanics and peasants. This cut me to the heart; but I could not help myself. The following circumstance, however, overcame me more than all: My father was a man of great knowledge and experience, but, like all old men, he remained faithful to the old method of practice. I visited many of his patients, and without telling me exactly what mode of treatment I was to pursue, he only observed, "You will act so and sohowever, I saw the patients had confidence in my father only, and not in me; they wished me to be his tool, and I therefore followed his mode of practice, and thus lost several of his patients, who could have been saved had I followed my own method.
- Among others, Doctor Caritens died during a momentary absence of my father, who recommended while stepping into his travelling chariot, to bleed the Doctor a second time. I did as he bid me, although convinced that emetics and opening medicine would cure the patient without fail; the Doctor died, and you may easily imagine the state of my feelings. I had just begun to publish a work on practical physic, but had no heart to finish it after this sad catastrophe. I betook myself again to philosophy. I wished daily to return to Gottingen, if I could do so with honour. I passed three years under such painful circumstances, when my friend Leisewitz invited me to go with him to Berlin, for which purpose his brother-in-law in Brunswick would advance me money to defray my expenses. Without much consideration, I accepted the invitation, and my portmanteau was soon ready.
- Arriving in Berlin, I found myself in my element, and began to breathe freely. Jerusalem and Lessing had given us letters of introduction to the greatest men in Berlin ; but they knew us already, Leisewitz as author of "Julius Von Tarent," and myself as author of my Dissertation. We had daily the choice of the first society; covers were laid for us in the first families daily, for dinner as well as supper. Von Zetlitz sent a general invitation that covers were laid for us every day during our stay in Berlin. Most of the time we could spare was divided between physicians and philosophers, of which the latter had the greater share. Spalding, Mendelsohn, Eberhard, Engel, Nicolai, Reichard, and Madame Bamberger, daughter of Doctor Sack, Bishop of Berlin, honoured us with their most sincere friendship. The latter, a highly gifted and accomplished lady, possessed the rare art of spreading over the most abstract hypothesis and theorem the brightest and most charming light; Jerusalem, the father of the ill-fated Werther (see the "Sorrows of Werther," by Goethe), used to send her his works to correct, and she alone was able to console and comfort him, when he was informed of the death of his beloved son. This amiable lady assumes in common life the character of a plain woman, and when at court, as friend of the Queen and the Princess Amalie, she won all hearts by her truly noble man ners and unconstrained courtesy: at court beloved, she was admired, nay, adored in the philosophical clubs. But do not think that here alone we spent all our time; Madame Bamberger knew how to blend study with amusement; she issued frequently cards of invitation to select parties, for suppers and balls, and her house was the point of union of all that was learned, beautiful, and amiable. Thus Berlin became my Paradise. I had the most tempting offers from the Minister of State to stay here; but the illness of my father obliged me, after a stay of three months, to return home. I visited Lessing on my journey back; stayed two days, which were the most interesting of all days I ever remember.
- It was now, I thought, high time to think earnestly of getting into good practice as a physician. I followed, in order to effect this, my own method; I cared not for criticism; good luck attended me; I was successful in many cases given up by others as hopeless. My father watched me now closely, but let me have free sway; he felt great pleasure at my success, and would now and then say, "Well done, my boy;" but nevertheless entreated of me not to offend a certain great personage; which, however, I frankly confessed I had already done, not caring much about it, as it was my intention not to stay in Celle. I wanted a greater sphere of action. My father's weakness and infirmity increased daily, which prevented him from visiting his patients, and determined him to give up altogether his practice, and to retire from a profession in which, during many years, he had so nobly done his duty; he informed his patients of it, telling them that they were perfectly free and at liberty to take the advice of his son, or any other physician, thereby insinuating, that in their choice they must not suffer themselves to be influenced by their feelings of friendship and regard towards him. Almost all his patients honoured me with their confidence.
- Now, my dear Philippine, a few words more. I am not rich; but my affairs are not in a deranged or desperate state, and were I to die to-day, and my property sold, it would fetch 5,000 dollars at least, so that I possess 2,000 dollars more than my father gave me. I have but 400 dollars salary; my practice is good, and becomes daily more lucrative; the income I derive from it now is more than sufficient to keep a good and respectable house; my prospects are flattering; but I can and must not name them at present; I will not bring them into account.
The Principles of Agriculture, 1844
Section I: The fundamental principles
- Agriculture is the art of deriving from the earth the most valuable organic productions. He who exercises this art, seeks to obtain profit by causing to grow, and by using, its animal and vegetable productions. The more considerable the gain derived, therefore, the better is the object accomplished. The most perfect agriculture is, evidently, that which produces, by the application of labour, the largest and the most permanent profit in comparison with the means employed. Systematic agriculture ought, then, to teach us all the circumstances by means of which we may derive the most considerable profit by the practice of the art.
- p. 1.
- The art of agriculture is the realization of some ideal object. lie who practises it has received from others, without considering the reasons on which it is founded, the idea or rule by which he proceeds. The skilful practice of an art consists, therefore, in the adoption of new ideas, in the study of new rules, and in judging the fitness of their being carried into practice.
- p. 2.
- The science of agriculture does not lay down any positive rules, but it develops the motives by which the best possible method of proceeding may be discovered and successfully pursued. In fact, the art executes some law given and received, but it is from science that law emanates.
- p. 2.
- The science of agriculture rests on experience; and nothing else should be required or expected from it but that which appertains to a practical science. The first principles arise from the perceptions of the senses; but if experience wholly and entirely flowed from these perceptions, the development would not be less the offspring of science and the work of the understanding.
- p. 3.
- An agricultural enterprise requires: 1st, a suitable person; 2nd, capital; 3rd, an estate.
- p. 8.
- Every person who seeks to practise agriculture with the full success which it admits—and that is the natural aim of every one who engages in it—must possess energy, activity, reflection, perseverance, and a knowledge of all the kindred and accessory sciences.
- p. 8.
- By capital we understand everything that, from the special use by the individual, or from its being placed at the disposal of others, produces a revenue or rent. We do not inquire into its origin, or ask whether it has been acquired by inheritance or by labour.
- p. 15.
Section II. The Economy, Organization and Direction of an Agricultural Enterprise
- The word " economy" has latterly been used in various senses; the Germans give it a very indefinite signification.
Judging from its etymology and original signification, the Greeks seem to have understood by it the establishment and direction of the menage, or domestic arrangements.
Xenophon, in his work on economy, treats of domestic management, the reciprocal duties of the members of a family and of those who compose the household; and only incidentally mentions agriculture as having relation to domestic affairs. This word is never applied to agriculture by Xenophon, nor, indeed, by any Greek author; they distinguish it by the terms, georgic geoponic.
The Romans give a very extensive and indefinite signification to the word "economy." They understand by it, the best method of attaining the aim and end of some particular thing; or the disposition, plan, and division of some particular work. Thus, Cicero speaks of oeconomia causae, oeconomia orationis; and by this he means the direction of a law process, the arrangement of an harangue. Several German authors use it in this sense when they speak of the oekonomie eines schauspiels, or eines gedichtes, the economy of a play or poem. Authors of other nations have adopted all the significations which the Romans have attached to this word, and understand by it the relation of the various parts of any particular thing to each other and to the whole—that which we are accustomed to term the organization. The word "economy" only acquires a real sense when applied to some particular subject: thus, we hear of "the economy of nature," "the animal economy," and " the economy of the state" spoken of. It is also applied to some particular branch of science or industry; but, in the latter case, the nature of the economy ought to be pointed out, if it is not indicated by the nature of the subject.
- p. 54-55.
- In speaking of agricultural management, the French say, I'economie rurale, and the English, rural economy; and yet neither the one nor the other intend thereby to signify the absolute execution of agricultural operations, but only the division and circumstances or appurtenances of agriculture. In Germany, where a Latin or Greek name has lately been thought to give dignity to a science, and has, consequently, been introduced into the title of most of the scientific works, some authors have begun to term, not only the science of agriculture, but agriculture itself, the oekonomie; and the word is used exclusively in this sense by many persons. It is for this reason that those who are supposed to practise the art with the greatest skill and science, are termed oekonomen (economists); and that some of those who are employed in superintending the labourers, even though they frequently have not the least idea of the actual principles of agriculture, chose to be designated by this title.
- p. 55.
Section III: Agronomy
- Agronomy ; or a Treatise on the Constituent Parts and Physical Properties of the Soil, and the best Method of acquiring a Knowledge of the different Earths, and ascertaining their Value.
- p. 258: Title and subtitle of section III of the book.
- It is the residue of animal and vegetable putrefaction, and is a black body; when dry it is pulverulent, and when wet has a soft, greasy feel... It is the produce of organic power—a compound of carbon, hydrogen, nitrogen, and oxygen, such as cannot be chemically composed.
- p. 336; Cited in: Edmund Ruffin An Essay on Calcareous Manures, Volume 1. J.W. Randolph, 1852. p. 85.
- Ruffin summarizes:
"Humus" is the term used by this author for the decomposed vegetable and other organic matter which is more or less mixed with all surface soil, and which gives to soil all its fertility, and furnishes all the food of plants.
- When humus remains constantly damp, without, however, being covered with water, it forms a very unpleasant smelling acid, which is more particularly, characterized by the property which it possesses of colouring blue litmus paper into red. This circumstance has long been known, and it is the reason that land and meadows which are not properly drained, and which exhibit these phenomena, are called sour. We have carefully examined these facts, and have endeavoured to discover the peculiar constitution of this acid. At first, we were inclined to regard it as being of a distinct nature, and having carbon for its base; but we have since become convinced that it is generally composed of acetic acid, and occasionally contains a portion of the phosphoric. This latter always adheres so firmly to the humus that it cannot be separated from it either by boiling or washing. The liquid in which the humus is boiled certainly acquires a slight acid flavour, but the greater part of the acid remains attached to the humus.
- This acid or sour humus it not at all of a fertilizing nature; on the contrary, it is prejudicial to vegetation* Where it is very strong and pervades the whole of the humus, the soil only produces reeds, rushes, sedge, and other useless, unpalatable plants; and whenever these abound, it may be inferred that the soil contains a great deal of sour or acid humus... There are various means of getting rid of this baneful property, and rendering the humus fertile. It is well known that with the aid of alkalies, ashes, lime, and marl, humus may be deprived of its acidity, and rendered easily soluble... Heaths do not thrive where this humus does not exist, and when they have established themselves in one particular spot, they suffer few other plants to appear. This humus may be changed by a dressing composed of marl, lime, or ammonia; and where this has been mixed with the soil, the heaths, &c., speedily perish.
- p. 343-4, as cited in Ruffin (1852, p. 85).
- In both the kinds of land we have been considering [i. e., classes of very fertile soil, rich in humus], we have supposed the humus to be mild, or exempt from acidity. J Sour or acid humus totally destroys the fertility of a soil; sometimes, however, the soil contains so very small a portion of acidity that its fertility is very slightly diminished, and only with regard to some few plants. Barley crops become more and more scanty in proportion as the acidity is increased; but oats do not appear to be at all affected by it. Rye grown on such land is peculiarly liable to rust, and is easily laid or lodged. The grains of all the oereals become larger, but contain less farina. Grass which grows on these spots is, both in species and taste, less agreeable, and less suitable for cattle, than any other, although it yields a very considerable produce in hay. In fact, in exact proportion with the increase of acidity, is the decrease of the value of the soil...
- p. 345, as cited in Ruffin (1852, p. 85).
- In the greater number of cases, peat is very much like acid or sour humus; indeed, it sometimes resembles it so strikingly that it is impossible to distinguish these substances apart.
- p. 349, as cited in Ruffin (1852, p. 85).
Quotes about Albrecht Thaer
- Thaer Principles of Agriculture, 2 vols. 4to. an excellent work. The author, though he never was in England, wrote on English husbandry so exactly that the board of agriculture in England sent him, by Mr. Sinclair, a patent as associate member of the Agricultural Society. He is a physician, but has now established a practical academy of husbandry near Berlin.
- Samuel Cooper Thacher, David Phineas Adams, William Emerson. The Monthly anthology, and Boston review. March 1811. p. 212.
- ln Prussia, the king especially patronizes agriculture. and the academy at Frankfort, upon the estate called Moegelin, under the superintendence of M. Thaer, the most scientific agriculturist in the world, is well known.
- The Cultivator, Volume 5. L. Tucker, 1838. p. 103.
- [Thaer's work offer] a great number of new ideas and useful directions, by connecting art with science, and introducing the theory of agriculture into the departments of natural history in general, and of chemistry in particular.
- Elie Victor Benjamin de Crud (1772-1845) French agronomist and translator of "The Principles of Agriculture" into French, cited in: Journal of Agriculture, Vol. 13. W. Blackwood., 1843, p. 480.
- Thaer's most well-known and systematic work, his four-volume Grundsatze der rationellen Landwirthschaft (Principles of Efficient Agriculture, 1809-1812), was reprinted throughout the nineteenth century and often translated, both in Europe and beyond. So formative were his research and publications that agrarian historians often refer to the early nineteenth century as the "Age of Thaer.
- Marion W. Gray (2000) Productive Men, Reproductive Women: The Agrarian Household and the Emergence of Separate Spheres During the German Enlightenment. p. 261.
- Thaer 200 Years at Möglin by Martin Frielinghaus and Claus Dalchow, 2007