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INTRODUCTION 
 
 TO THE STUDY OF 
 
 THE SCIENTIFIC PRINCIPLES 
 
 OF 
 
 AGRICULTURE; 
 
 BEING 
 
 Delivered May 6, 1884, 
 AT THE UNIVERSITY MUSEUM, OXFORD, 
 
 BY 
 
 JOSEPH HENRY GILBERT, M.A., Ph.D., LL.D., 
 
 SIBTHORPIAN PROFESSOR OP RURAL ECONOMY IN THE 
 UNIVERSITY OF OXFORD ; . 
 
 Vice-President of the Chemical Society ; Fellow of the Royal, Linnean, and Royal Meteorological 
 
 Societies; Honorary Member of the Royal Agricultural Society of England, of the 
 
 ChemicO'AgricuUural Society of Ulster, and of the Academy of Agriculture and 
 
 Forestry of Petrovskoie ; Corresponding Member of the institute of France 
 
 {Academy of Sciences), of the Society of Agriculturists of France, 
 
 and of the Agricultural Institute of Gorigoretsk ; Chevalier 
 
 du Mr rite Agricole (France); and Gold Medallist Of 
 
 Merit for Agriculture (Emperor of Germany). 
 
 LONDON : HENRY FROWDE, 
 OXFORD UNIVERSITY PRESS WAREHOUSE, AMEN CORNER, E.G. 
 
 1884. 
 
 [ Price One Shilling. ] 
 
INTKODUCTION 
 
 TO THE STUDY OF 
 
 THE SCIENTIFIC PRINCIPLES 
 
 OF 
 
 AGRICULTURE; 
 
 BEING 
 
 Deliveeed May 6, 1884, 
 AT THE UNIVERSITY MUSEUM, OXFORD, 
 
 BY 
 
 JOSEPH HENRY GILBERT, M.A., Ph.D., LL.D., 
 
 SIBTHORPIAN PROFESSOR OP RURAL ECONOMY IN THE 
 UNIVERSITY OP OXFORD ; 
 
 Vice-President of the Chemical Society ; Fellow of the Royal, Linnean, and Royal Meteorological 
 
 Societies; Honorary Member of the Royal Agricultural Society of England, of the 
 
 Chanico- Agricultural Society of Ulster, and of the Academy of Agriculture and 
 
 Forestry of Petrovskoie ; Corresponding Member of the Institute of France 
 
 (Academy of Sciences), of the Society of Agriculturists of France, 
 
 and of the Agricultural Institute of Gorigoretsk ; Chevalier 
 
 du Me" rite Agricole, (France) ; and Gold Medallist of 
 
 Merit for Agriculture (Emperor of Germany). 
 
 LONDON : HENRY FROWDE, 
 
 OXFORD UNIVERSITY PRESS WAREHOUSE, AMEN CORNER, E.C. 
 
 1884. 
 
LOAN STACK 
 
 Giro 
 
%5* 
 
 INAUGURAL LECTURE. /8 ^ 
 
 Km 
 
 Oxford, May 6, 1884. 
 
 Mr. Vice-Chancellor and Gentlemen, 
 
 The term 'Rural Economy, which gives the title to 
 the Professorship to which I have been appointed, 
 might be held to include such a variety of topics, that 
 if I had no other guide in the selection of subjects to 
 bring before you, I should be placed in a position of 
 some difficulty. It would not be inappropriate to 
 treat of the general management of landed property 
 from the point of view of the Land-owner or the 
 Land-agent ; of the practical details of farming, 
 mechanical, economical, and commercial, such as are 
 essential to be observed by the tenant or occupier, if 
 his " business is to be a profitable one ; or, lastly, 
 attention might be confined to the elucidation of the 
 scientific principles involved in successful practice, so 
 far as the existing knowledge of the day permitted. 
 
 Fortunately, however, I have not only the obvious 
 intentions of the Founder of this Chair, the late 
 Professor Sibthorp, and the way in which my Pre- 
 decessor, the late Professor Daubeny, interpreted and 
 performed the duties of the office, to guide and limit 
 my selection of subjects ; but, on the 14th of July last, 
 these duties were, under the sanction of the Chancery 
 Division of the High Court of Justice, defined to be 
 to lecture on the Scientific Principles of Agriculture, 
 
 It may be not out of place to remind you that, 
 according to Dr. Sibthorp's will, the Sherardian Pro- 
 fessor of Botany for the time being was to hold the 
 Professorship of Rural Economy ; and that hitherto, 
 
 B 
 
 147 
 
2 THE SCIENTIFIC PRINCIPLES 
 
 that is until the settlement by the Court of Chancery 
 last year, the appointment has been so held ; and the 
 obligation was limited to giving one Public Lecture in 
 each term. The new arrangement, however, dissociates 
 the Chair of Rural Economy from that of Botany, and 
 requires that twelve lectures shall be given annually. 
 
 Thus my responsibilities are somewhat defined, and 
 they are, at the same time, somewhat limited : — for, 
 how far from a complete system of instruction in all 
 that pertains to Rural Economy can be embodied in 
 a course of twelve lectures may be judged by reference 
 to the course of study laid down in Institutions 
 specially devoted to the training of Students in 
 Agriculture. Thus, the Syllabus of one Agricultural 
 College includes no less than thirty distinct subjects 
 of lecture or other instruction, and the Prospectus of 
 another enumerates sixteen main departments, cover- 
 ing much the same range of subjects as the other ; 
 whilst each Institution has a numerous staff of Pro- 
 fessors or Teachers. Again, in one London College a 
 course of forty lectures is annually given on Soils, 
 Manures, Crops, Live Stock, &c. ; and in another lectures 
 and laboratory instruction are given on Soils, Rota- 
 tion, Manures, Feeding and Feeding-stuffs, Seeds, &c. 
 
 It is not then, I take it, expected of me that I 
 should undertake to impart that systematic instruc- 
 tion in the various branches of the art and the science 
 of Agriculture, which it is desirable the student who 
 intends to devote himself to the details of practical 
 farming, whether as agent or occupier, should receive. 
 I assume that those studying at this University will 
 for the most part be interested in land either as 
 Owners, or as Clergymen in rural districts, or it may 
 be as Statesmen, and that it should be my endeavour 
 so to inculcate general principles as to train the 
 
OF AGRICULTURE. 3 
 
 observation, and give a direction to the reflections, of 
 those who hear me, and to enable, and it may be to 
 stimulate them, to study further for themselves, as 
 problems requiring it may come before them. 
 
 What then is Agriculture — the scientific principles 
 of which we have to investigate 1 Discarding the 
 mere etymological meaning of the term, and giving it 
 the 'wider signification accorded to it by long usage, it 
 is the art by which animal as well as vegetable pro- 
 ducts are obtained from the land. 
 
 Natural vegetation, as in the case of prairie-lands, 
 for example, does indeed contribute food to the lower 
 animals, and through them food and other products 
 for the use of man ; but the result is attained with 
 little of his aid which can come under the definition 
 of Agriculture. 
 
 But the practices by which vegetable and animal 
 products are obtained from the land in settled coun- 
 tries differ essentially from those above alluded to, 
 and it is these to which our attention must mainly be 
 directed. Such Agriculture implies the growth of 
 other plants than would be obtained under conditions 
 of natural vegetation, and the growth of more pro- 
 duce over a given area than would be so obtained. 
 It implies, in fact, what may be called concentrated 
 production. 
 
 Agriculture, the oldest of the arts, was in methods 
 at first purely mechanical ; though, as we now know, 
 the results to be attained were largely chemical. 
 When manure was first applied to the soil, that is 
 when the refuse of previous crops, or the excrements 
 of animals, were first returned to the land as a means 
 of increasing the growth of succeeding crops, directly 
 chemical means — the supply of material — were first 
 adopted. 
 
 b i 
 
4 THE SCIENTIFIC PRINCIPLES 
 
 Professor Daubeny, in his lectures on Roman 
 Agriculture, quotes Cato as having said — 
 
 ' If I am asked, what is the first point in good hus- 
 bandry, I answer, good ploughing ; what the second, 
 ploughing of any kind ; what the third, manuring/ 
 
 We have thus evidence of the relatively little 
 esteem in which manuring was held in Italy two 
 thousand years ago ; and in the fact that so much 
 more value was set upon the mechanical operations 
 we have evidence that the resources of the soil itself 
 were far from being exhausted, and only required 
 such means to be taken to render them available. 
 
 There is nevertheless evidence that, long before the 
 time of Cato, it was sought to restore fertility to the 
 soil by practices the efficacy of which is still fully 
 recognised ; though the explanation of some of the 
 phenomena involved is still a matter of controversy. 
 Such, for example, was the growth of various crops of 
 the Leguminous family, sometimes to be in great part 
 removed, but in others to be at once ploughed into 
 the land, by either of which methods the growth of 
 succeeding crops was enhanced. This subject will 
 receive detailed consideration further on. 
 
 But although manuring, in various ways, has thus 
 been so long recognised as desirable, it is in fact only 
 in quite recent times that the rationale of such prac- 
 tices could be at all satisfactorily explained. To this 
 end it was obviously essential not only to know the 
 composition of the vegetable products grown, but 
 something of the sources of their various constituents 
 — whether these must be derived from the soil, or 
 whether from the atmosphere, or from water % 
 
 What then is the composition, and what are the 
 sources of the constituents of vegetable products \ 
 
 When a vegetable (or animal) substance is burnt, 
 
OF AGRICULTURE. 5 
 
 the greater part of it is dissipated, but there remains 
 a white ash. This ash is found on analysis to contain 
 most or all of the constituents enumerated in the 
 first column of the following Table. 
 
 Constituents of Plants and Animals. 
 
 Incombustible or 
 
 Combustible or 
 
 Fixed. 
 
 Volatile. 
 
 Iron. 
 
 Carbon. 
 
 (Manganese). 
 
 Hydrogen. 
 
 Lime. 
 
 Oxygen. 
 
 Magnesia. 
 
 Nitrogen. 
 
 Potash. 
 
 
 Soda. 
 
 
 Phosphoric acid. 
 
 
 Sulphuric acid. 
 
 
 Chlorine. 
 
 
 Silica. 
 
 
 Sulphur. 
 Phosphorus. 
 
 Barer substances than these are also sometimes 
 found. It will be my duty, in subsequent lectures, 
 to call your attention in some detail to what is 
 known as to the occurrence, and the offices, of the 
 various mineral or ash -constituents in plants. It 
 will suffice here to say, that the ash of one and the 
 same description of plant, growing on different soils, 
 may, so long as it is in the vegetative or immature 
 state, differ very much in composition. Again, the 
 ashes of different species, but growing on the same 
 soil, will differ very widely in the proportion of their 
 several constituents. But it is found that the nearer 
 we approach to the elaboration of the final products 
 of the plant — the seed for example — the more fixed 
 is the composition of the ash of such products of one 
 and the same species. In other words, there is very 
 
6 THE SCIENTIFIC PRINCIPLES 
 
 little variation in the composition of the ash of one 
 and the same description of seed, or other final pro- 
 duct, provided it be evenly and perfectly matured. 
 This fact alone, independently of what has been 
 established of late years in regard to the office or func- 
 tion so to speak of individual mineral constituents of 
 plants, would be sufficient to indicate the essentialness 
 of such constituents for healthy growth. 
 
 Th. De Saussure, in his work entitled, * Eecherches 
 sur la Vegetation'/ published in 1 804, gave the re- 
 sults of the analyses of many plant-ashes, maintained 
 the essentialness of the ash-constituents, and pointed 
 out that they must be derived from the soil. He 
 a] so called attention to the probability that the 
 incombustible constituents so derived by plants from 
 the soil were the source of those found in the 
 animals which fed upon them. 
 
 Yet such was the prevailing uncertainty on the 
 point, that Sir Humphrey Davy, in his lectures 
 delivered not long afterwards, deemed it not inap- 
 propriate to combat the idea that the earths found 
 in plants had been formed from any of the elements 
 existing in the air, or in water. After quoting the 
 results of an experiment of his own, in which he 
 attempted to grow oats without any supply of silica 
 beyond that contained in the seed sown, and referring 
 to the experiments of De Saussure, he says : — 
 
 ' As the evidence on the subject now stands, it- 
 seems fair to conclude, that the different earths and 
 saline substances found in the organs of plants are 
 supplied by the soils in which they grow ; and in no 
 cases composed by new arrangements of the elements 
 in air or water/ 
 
 It is no longer doubted that the mineral or ash- 
 constituents of plants must be provided within the 
 
OF AGRICULTURE. 7 
 
 soil, either from its own natural resources, or by 
 means of manure. It will be seen, however, from 
 the facts just stated, how very recently fixed ideas 
 on the subject have been arrived at. 
 
 Then, as to the combustible or volatile constituents 
 which are expelled in the incineration — the carbon, 
 the hydrogen, the oxygen, and the nitrogen. From 
 what we now know of the sources of these con- 
 stituents of plants, it is obvious that a knowledge of 
 the composition of the atmosphere and of water was 
 essential to any true conception of the main features 
 of the vegetative process, and it was only towards 
 the end of the last century that the composition of 
 the air, and of water, and their mutual relations with 
 vegetation, were first pointed out. 
 
 I shall have to go into these matters in some 
 detail in subsequent lectures, but I would here 
 observe that it is to the collective labours of Black, 
 Scheele, Priestley, Lavoisier, Cavendish, and Watt, 
 that we owe the knowledge that common air consists 
 of nitrogen and of oxygen, with a little carbonic acid ; 
 that carbonic acid itself is composed of carbon and 
 of oxygen ; and that water is composed of hydrogen 
 and oxygen ; whilst Priestley and Ingenhousz, Sen- 
 nebier and Woodhouse, investigated the mutual re- 
 lations of these bodies and vegetable growth. 
 
 Thus, Priestley observed that plants possessed the 
 faculty of purifying air vitiated by combustion, or 
 by the respiration of animals ; and he having dis- 
 covered oxygen, it was found that the bubbles which 
 Bonnet had shown to be emitted from the surface of 
 leaves immersed in water consisted chiefly of that 
 gas. Ingenhousz demonstrated that the action of 
 light was essential to the development of these 
 phenomena, and Sennebier proved that the oxygen 
 
THE SCIENTIFIC PRINCIPLES 
 
 evolved resulted from the decomposition of the 
 carbonic acid taken up. 
 
 So far, attention had been more prominently- 
 directed to the influence of plants upon the media 
 with which they were surrounded, than to that of 
 those media in contributing to the increased sub- 
 stance of the plants themselves. 
 
 It was, too, towards the end of the last century, 
 and in the beginning of the present one, that De 
 Saussure followed up these enquiries ; and, in his 
 work already alluded to, he may be said to have 
 indicated, if not indeed established, some of the most 
 important facts with which we are yet acquainted 
 regarding the sources of the constituents of the 
 growing plant. He illustrated experimentally, and 
 even to a certain extent quantitatively, the fact that 
 in sun-light plants increase in carbon, hydrogen, and 
 oxygen, at the expense of carbonic acid and of 
 water ; and in his main experiment on the point he 
 found the increase in carbon, and in the elements of 
 water, was very closely in the proportion in which 
 they are known to exist in the chief non-nitrogenous 
 constituents of plants, the carbohydrates — starch, 
 gum, sugar, cellulose, etc. 
 
 With regard to the nitrogen which plants had 
 already been shown to contain, Priestley and Ingen- 
 housz thought their experiments indicated that they 
 absorbed free nitrogen from the atmosphere ; but 
 Sennebier and Woodhouse arrived at an opposite 
 conclusion. De Saussure, again, thought that his 
 experiments showed rather an evolution of nitrogen 
 at the expense of the substance of the plant than 
 any assimilation of it from gaseous media. He 
 further concluded that the source of the nitrogen of 
 plants was more probably the nitrogenous compounds 
 
OF AGRICULTURE. 9 
 
 within the soil, and the small amount of ammonia 
 which he demonstrated to exist in the atmosphere. 
 
 Upon the whole, De Saussure concluded that air 
 and water contributed a much larger proportion of 
 the dry substance of plants than did the soils in 
 which they grew. In his view a fertile soil was one 
 which yielded liberally to the plant nitrogenous 
 compounds, and the incombustible or mineral con- 
 stituents ; whilst the carbon, hydrogen, and oxygen, 
 of which the greater proportion of the dry substance 
 of the plant was made up, were at least mainly 
 derived from the air and water. 
 
 From what has been stated, it will be seen that 
 anything like a consistent scientific explanation of 
 vegetable and animal production was impossible 
 until comparatively very recent times. In fact it is 
 clear that agricultural chemistry properly so called 
 is not a century old ; whilst, without a knowledge of 
 it, the scientific principles of agriculture could not be 
 taught. 
 
 What then is agricultural chemistry 1 It is the 
 chemistry of the soil, the chemistry of the atmo- 
 sphere, the chemistry of vegetation, and the chemistry 
 of animal life and growth, in their bearings on 
 agricultural production. 
 
 Obviously vegetable and animal physiology are 
 essential elements in the explanation of many of the 
 phenomena of agricultural production ; but for any- 
 thing more than necessary passing reference to these 
 branches of science you must look to the distin- 
 guished Professors of Physiology and Botany now 
 attached to this University. 
 
 To Sir Humphrey Davy we owe the first sys- 
 tematic attempt to apply scientific principles to the 
 elucidation and improvement of agricultural practice. 
 
10 THE SCIENTIFIC PRINCIPLES 
 
 Each year, for ten successive years, from 1802 to 
 
 181 2, he delivered a course of lectures which, in 
 
 18 1 3, were published in a work entitled, 'Elements 
 of Agricultural Chemistry/ which he finally revised 
 for the fourth edition in 1827, but which has gone 
 through several editions since. 
 
 In those lectures Sir Humphrey Davy passed in 
 review and correlated the then existing knowledge, 
 both practical and scientific, bearing upon agriculture. 
 He treated of the influences of heat and light ; of the 
 organisation of plants ; of the difference, and the 
 change, in the chemical composition of their different 
 parts ; of the sources, composition, and treatment of 
 soils ; of the composition of the atmosphere, and its 
 influence on vegetation ; of the composition and the 
 action of manures ; of fermentation and putrefaction ; 
 and, finally, of the principles involved in various 
 recognised agricultural practices. 
 
 Concurrently with the delivery and the publication 
 of Davy's Lectures in England, the most prominent 
 writer on the scientific principles of agriculture on 
 the continent was Thaer. In 18 10 he published a 
 work entitled ' Principes Eaisonnes d' Agriculture/ 
 and for some years afterwards contributed papers on 
 some special points. He considered that the fertility 
 of the soil depended on the amount and character 
 of the humus it contained ; it being, in his view, the 
 only substance, excepting water, that yielded aliment 
 to plants. He pointed out that it was the residue 
 of previous vegetation, containing carbon, hydrogen, 
 oxygen, and nitrogen, associated with phosphorus, 
 sulphur, and some salts. He quotes De Saussure 
 as having shown that humus contains a lower per- 
 centage of oxygen and higher percentages of carbon 
 and nitrogen than the plants from which it has been 
 
OF AGRICULTURE. 11 
 
 produced. He states that its composition varies 
 according to the access of oxygen and water ; that 
 it absorbs oxygen, and gives out carbonic acid, which 
 supplies nourishment to plants ; also, that it yields 
 soluble extractive matter again and again by time 
 and exposure. He further states that the more the 
 decomposition has proceeded, the more refractory, and 
 the less active and useful for vegetation, is the residue. 
 
 With the exception of the discourses of Sir 
 Humphrey Davy, and the writings of Thaer, the 
 subject seems to have received comparatively little 
 attention, nor was any other addition of importance 
 made to our knowledge in regard to it, during a 
 period of more than twenty years, from the date of 
 the appearance of De Saussure's work in 1 804. 
 
 From about 1825 to 1840, Dr. Carl Sprengel, for- 
 merly Professor of Agriculture at Brunswick, pub- 
 lished a series of about thirty papers in connection 
 with agriculture, and agricultural chemistry. These 
 memoirs covered a wide range of subjects, and re- 
 corded the results of numerous investigations by the 
 author himself. Among them may be mentioned in- 
 vestigations on humus, humic acid, and humates ; on 
 the constituents of some surface soils and subsoils ; 
 on the composition of various kinds of straw, and 
 their value as food and litter ; on the amount of 
 potash in granites, and other rocks ; on the ash- 
 constituents of cereal grains, &c. Lastly, he published 
 a general treatise on manures, including a chapter on 
 animal manures, in which he gives the results of the 
 analysis of the solid and liquid excretions of the 
 various animals of the farm, and, among other points, 
 insists upon the value as manure of the ammonia 
 yielded by such materials. 
 
 Professor Schiibler, of Tubingen, also published 
 
12 THE SCIENTIFIC PRINCIPLES 
 
 a Work entitled, 'Grundsatze der Agricultur-Chemie/ 
 a second and revised edition of which was brought 
 out in 1838, by Professor Krutzsch, of Tharand. In 
 this Work the physical and chemical properties of 
 soils are discussed in much detail ; and the results of 
 numerous investigations on the subject by the author 
 himself are given. 
 
 Boussingault, who had previously published nu- 
 merous papers, chiefly on chemical subjects, about 
 1834 became, by marriage, joint proprietor with his 
 brother-in-law of the estate of Bechelbronn, in Alsace. 
 His brother-in-law, M. Lebel, was both a chemical 
 manufacturer and an intelligent practical farmer, 
 accustomed to use the balance for the weighing of 
 manure, crops, and cattle. Boussingault at once 
 applied himself to Chemico- Agricultural research ; 
 and it was under these conditions of the association 
 of f Practice with Science ' that the first laboratory 
 on a farm was established. 
 
 From this time forward, Boussingault generally 
 spent about half the year in Paris, and the other 
 half in Alsace; and he has continued his scientific 
 labours, sometimes in the city and sometimes in the 
 country, up to the present time. I may here men- 
 tion that I had the pleasure of seeing him well, 
 and still actively interested in problems of agricul- 
 tural science, at his Chateau in Alsace in the autumn 
 of last year. 
 
 Boussingault's first important contribution to agri- 
 cultural chemistry was made in 1836, when he 
 published a paper on the amount of nitrogen in 
 different foods, and on the equivalence of the foods, 
 founded on the amounts of nitrogen they contained ; 
 and he compared the results so arrived at with the 
 estimates of others founded on actual experience. 
 
OF AGRICULTURE. 13 
 
 Although his conclusions on the subject have doubt- 
 less undergone modification since that time, the work 
 itself marked a great advance on previously existing 
 knowledge and modes of viewing the question. 
 
 In 1837 Boussingault published papers on the 
 amount of gluten in different kinds of wheat ; on 
 the influence of the clearing of forests on the diminu- 
 tion of the flow of rivers ; and on the meteorological 
 influences affecting the culture of the vine. In 1838 
 he published the results of an elaborate research on 
 the principles underlying the value of a rotation of 
 crops. He determined by analysis the composition, 
 organic and inorganic, of both the manures applied 
 to the land, and the crops harvested. In his treat- 
 ment of the subject he evinced a clear perception 
 of the most important problems involved in such 
 an enquiry ; some of which, with the united labours 
 of himself and many other workers, have scarcely yet 
 received an undisputed solution. 
 
 Thus, in the same year (1838), he published the 
 results of an investigation on the question whether 
 plants assimilate the free or uncombined nitrogen 
 of the atmosphere ; and although the analytical 
 methods of the day were inadequate to the decisive 
 settlement of the point, his conclusions were in the 
 main those which much subsequent work of his own, 
 and much of others also, have served to confirm. 
 
 In subsequent lectures I shall have to refer in 
 some detail to the various investigations here 
 alluded to. 
 
 As a further element of the question of the chemical 
 statistics of rotation, Boussingault determined the 
 amount and composition of the residues of various 
 crops ; also the amount of constituents consumed in 
 the food of a cow, and of a horse, respectively, and 
 
14 THE SCIENTIFIC PRINCIPLES 
 
 yielded in the milk and excretions of the cow, and 
 in the excretions of the horse. Here, again, tha 
 exigencies of the investigation he undertook were 
 beyond the reach of the known chemical methods 
 of the time. Indeed, rude as the art of agriculture 
 is generally considered to be, the scientific elucida- 
 tion of its practices requires the most refined and 
 very varied methods of research ; and a characteristic 
 of the work, not only of Boussingault, but of most 
 agricultural investigators, may be said to be, that 
 they have frequently had to devise methods suitable 
 to their purpose, before they could grapple with the 
 problems before them. 
 
 In 1839, chiefly in recognition of his important 
 contributions to agricultural chemistry, Boussingault 
 was elected a member of the Institute of France ; 
 and in 1878, thirty-nine years later, the Council of 
 the Eoyal Society awarded to him the Copley Medal, 
 the highest honour at their disposal, for his numerous 
 and various contributions to science, but especially 
 for those relating to agriculture. 
 
 The foregoing brief historical sketch is sufficient 
 to indicate, though but in broad outline, the range 
 of existing knowledge on the subject of agricultural 
 chemistry prior to the appearance of Liebig's me- 
 morable work, ' Organic Chemistry in its applications 
 to Agriculture and Physiology,' the first edition of 
 which was published in 1840. 
 
 It will be seen that some very important, and indeed 
 fundamental, facts had already been established in 
 regard to vegetation ; first by the numerous investi- 
 gations made about half a century previously, by which 
 the composition of the atmosphere, and of water, and 
 the mutual relations of these and vegetable growth, 
 
OF AGRICULTURE. 15 
 
 had been determined ; next by the labours of De 
 Saussure, to which we owe a near approach to a quan- 
 titative representation of the phenomena of vege- 
 tation, which had thus far only been qualitatively 
 observed. To De Saussure we also owe a clear per- 
 ception of the importance, and of the sources, of both 
 the nitrogen, and the ash-constituents, of plants. Then 
 followed Davy, with the first attempt to give a sys- 
 tematic view of the relations of practice with science 
 in agriculture ; Thaer, who traced the fertility of 
 soils to the residue of previous vegetation which they 
 contained ; Sprengel, who contributed much experi- 
 mental result on various branches of the subject ; and 
 lastly Boussingault, who had not only still further 
 extended experimental enquiry, but brought both 
 his own and previous results to bear upon the eluci- 
 dation of long-recognised agricultural practices. 
 
 There can be no doubt that the data supplied by 
 the researches which have been referred to, and espe- 
 cially those of De Saussure, Davy, Thaer, Sprengel, 
 and Boussingault, contributed important elements to 
 the basis of established facts upon which Liebig 
 founded his brilliant generalisations. Indeed, so ob- 
 vious was this, that, in 1841, Dumas and Boussingault 
 published, jointly, an essay which afterwards appeared 
 in English under the title of ' The Chemical and 
 Physiological Balance of Organic Nature,' which was, 
 in fact, a sort of ' reclamation/ 
 
 Nor can there be any doubt that the appearance 
 of Liebig's two works, ' Organic Chemistry in its 
 applications to Agriculture and Physiology' in 1840, 
 and * Animal Chemistry, or Organic Chemistry in its 
 applications to Physiology and Pathology' in 1842, 
 constituted a very marked epoch in the history of 
 the progress of Agricultural Chemistry. In the 
 
16 THE SCIENTIFIC PRINCIPLES 
 
 treatment of his subject he not only called to his aid 
 the previously existing knowledge directly bearing 
 upon it, but he also turned to good account the more 
 recent triumphs of organic chemistry, many of which 
 had been won in his own laboratory. Further, a 
 marked feature of his expositions was the adoption of 
 the quantitative method of illustration, and argument. 
 But, notwithstanding the evidence afforded by the 
 direct experiments of De Saussure and his prede- 
 cessors, Vegetable Physiologists, and some others, con- 
 tinued to hold the view that the humus of the soil 
 was the source of the carbon of vegetation. Liebig 
 gave full weight to the evidence of the experiments 
 of De Saussure and others; he illustrated the pos- 
 sible or probable transformations within the plant 
 by facts already established in organic chemistry ; 
 and he demonstrated the impossibility of the humus 
 of the soil supplying the amount of carbon assimi- 
 lated over a given area. He pointed out, that 
 humus itself was the product of previous vegetable 
 growth; that it could not therefore be an original 
 source of the carbon ; and that, from the degree of 
 its insolubility, either in pure water or in water con- 
 taining alkaline or earthy bases, only a small portion 
 of the carbon assimilated by plants could be derived 
 from the amount of humus that could possibly enter 
 the plant in solution. He maintained that, so far as 
 humus was beneficial to vegetation at all, it was 
 only by its oxidation, and a consequent supply of 
 carbonic acid within the soil ; a source which he 
 considered only of importance in the early stages 
 of the life of a plant, and before it had developed, 
 and exposed to the atmosphere, a sufficient amount 
 of green surface to render it independent of soil- 
 supplies of carbonic acid. 
 
OF AGRICULTURE. 17 
 
 In subsequent lectures, evidence will be adduced 
 showing that Liebig was certainly right, in concluding 
 that humus is not an adequate source of the carbon 
 of our crops. It will be seen that, to some of them at 
 any rate, it is at most only a very limited source, if 
 indeed it is to them a source at all. It will, on the 
 other hand, be shown that the organic residue of pre- 
 vious vegetation accumulated in the soil is, to say the 
 least,a very material source of the nitrogen of our crops. 
 
 Thus, though mistaken as to the explanation of 
 the fertility of soils rich in humus, Thaer and 
 others were, after all, not far from the truth w r hen 
 they maintained that the richness of a soil in such 
 matter in a condition readily susceptible to oxidation, 
 was, in a great degree, the measure of its fertility. 
 
 With regard to the hydrogen of plants, at any 
 rate that portion of it contained in their non- 
 nitrogenous products, Liebig maintained that its 
 source must be water; and that the source of the 
 oxygen was either that contained in carbonic acid, or 
 that in water. 
 
 With regard to the nitrogen of vegetation, both 
 from the known characters of free nitrogen, and as 
 he considered a legitimate deduction from direct 
 experiments, Liebig argued that plants did not 
 assimilate uncombined nitrogen, either from the 
 atmosphere, or dissolved in water and so absorbed by 
 the roots. The source of the nitrogen of vegetation 
 was, he maintained, ammonia ; the product of the 
 putrefaction of one generation of plants and animals 
 affording a supply for its successors. He pointed 
 out that, in the case of a farm receiving nothing 
 from external sources, and selling off certain products, 
 the amount of nitrogen in the manure produced by 
 the consumption of some of the vegetable produce on 
 
18 THE SCIENTIFIC PRINCIPLES 
 
 the farm itself, together with that due to the refuse 
 of the crops, must always be less than was contained 
 in the crops grown. He concluded that, although 
 the quantity returned to the land as manure was 
 important, a main source of the nitrogen assimilated 
 over a given area was the ammonia brought down 
 from the atmosphere in rain. 
 
 There can be no doubt that, owing to the limited 
 and defective experimental evidence then at command 
 on the point, Liebig at that time (as he did afterwards) 
 greatly over-estimated the amount of combined ni- 
 trogen available to vegetation from that source. 
 
 In Boussingault's • reclamation ' already referred 
 to, he gave much more prominence to the importance 
 of the nitrogen of manures. In Liebig's next edition 
 (in 1843) he combated the notion of the relative 
 importance of the nitrogen of manures. He main- 
 tained, in opposition to the view put forward in his 
 former edition, that the atmosphere afforded a 
 sufficient supply of combined nitrogen not only for 
 natural vegetation, but for cultivated plants ; that 
 this supply was sufficient for the cereals as well as 
 for leguminous plants ; that it was not necessary to 
 supply nitrogen for the former ; and he insisted very 
 much more strongly than formerly, on the relative 
 importance of the supply of the incombustible, or, 
 as he designated them, the ' inorganic = or ' mineral/ 
 constituents. 
 
 Many determinations of the amount of combined 
 nitrogen brought down in rain have been made, in 
 different countries, since the date here referred to ; 
 and in a subsequent lecture it will be shown that 
 the amount so available to the vegetation of a given 
 area is very much less than was assumed by Liebig, 
 or has generally been supposed. 
 
OF AGRICULTURE. 19 
 
 As to the incombustible, or, as he designated them, 
 the ' miner aV constituents, Liebig adduced many 
 illustrations in proof of their essentialness. He 
 called attention to the variation in the composition 
 of the ash of plants grown on different soils ; and he 
 assumed a greater degree of mutual replaceability of 
 one base by another, or of one acid by another, than 
 could now be admitted. He traced the difference in 
 the mineral composition of diiferent soils to that of 
 the rocks which had been their source ; and he seems 
 to have been led by the consideration of the gradual 
 action of ' weathering,' in rendering available the 
 otherwise locked-up stores, to attribute the benefits 
 of fallow exclusively to the increased supply of the 
 incombustible or mineral constituents which would, 
 by its agency, be brought into a condition in which 
 they could be taken up by plants. 
 
 It will be seen further on, how very materially 
 subsequently acquired experimental evidence has 
 tended to modify our views as to the explanation of 
 the benefits of fallow. 
 
 The benefits of an alternation of crops, Liebig 
 considered to be in part explained by the influence 
 of the excreted matters from one description of crop 
 upon the growth of another. He did not attach 
 weight to the assumption that such matters would 
 be directly injurious to the same description of crop ; 
 but he supposed rather that the matters excreted by a 
 plant were those which it did not need, and that they 
 would therefore be of no avail to the same description 
 of plant, but would be of use to others. He, how- 
 ever, attributed much of the benefits of a rotation, to 
 different mineral constituents being required from 
 the soil by the different crops. 
 
 Since the enunciation of these views, very much 
 
 c % 
 
20 THE SCIENTIFIC PRINCIPLES 
 
 direct experimental evidence bearing upon the 
 rationale of rotation has been acquired, and it 
 will be my duty to lay it before you in some 
 detail. 
 
 Treating of manure, Liebig laid the greatest stress 
 on the return by it of the potass and the phosphates 
 removed by the crops. But, in his first edition, he 
 also insisted on the importance of the nitrogen, 
 especially that in the liquid excretions of animals, 
 and condemned the methods of treatment of animal 
 manures by which the ammonia was allowed to be 
 lost by evaporation. It is curious, and significant, 
 however, that some of the passages in that edition, 
 in which he the most forcibly urges the value of the 
 nitrogen of animal manures, are omitted in the third 
 and fourth editions. 
 
 In his second work, that on Animal Chemistry, 
 published in 1842, Liebig discussed two subjects of 
 much interest and practical importance to the agri- 
 culturist : — namely, the sources in the food of the fat 
 stored up in the animal body, and the characteristic 
 food requirements of the animal organism induced by 
 the exercise of force. 
 
 To render the points here at issue intelligible, it is 
 necessary to remind you that the constituents of 
 food, both vegetable and animal, may broadly be 
 classed into those containing nitrogen, and those not 
 containing it — in other words, into the nitrogenous, 
 and the non-nitrogenous constituents. 
 
 From the nitrogenous constituents of the food, the 
 nitrogenous constituents of the animal body — the 
 membranes and cellular tissue, the nerves and brain, 
 cartilage, and the organic part of bones — must be 
 derived. It is admitted that by oxidation and 
 transformation within the bodv, some of these nitro- 
 
OF AGKICULTURE. 21 
 
 genous matters may yield fat, with other products, 
 such as urea which passes off by the urine, and 
 carbonic acid which passes off by respiration. 
 
 The non-nitrogenous constituents of the food on 
 the other hand — the fatty matters, and the so-called 
 carbohydrates — starch, sugar, cellulose, &c, are sup- 
 posed to be the chief sources of the carbonic acid 
 respired, and hence have sometimes been classed as 
 the respiratory constituents of food. 
 
 The questions arise — Is the non-nitrogenous sub- 
 stance fat, which is stored up in the feeding of the 
 herbivora, derived chiefly from the nitrogenous 
 matters of the organs, or in the circulation, or from 
 the non-nitrogenous matters of the food, the carbo- 
 hydrates 1 Then, again, in the exercise of force, is 
 the increased amount of the products of oxidation 
 eliminated from the bodv chieflv due to an increased 
 transformation of the nitrogenous substance of the 
 tissues and fluids, or of the non-nitrogenous con- 
 stituents — the fat of the body, or of the food, and 
 the carbohydrates \ 
 
 In reference to the sources of the fat of the animal 
 body, Liebig maintained that the vegetable food 
 consumed by herbivora did not contain anything 
 like the amount of fat which they stored up in 
 their bodies ; and he showed how nearly the com- 
 position of fat was obtained by the simple elimina- 
 tion of so much oxygen, or of oxygen and a little 
 carbonic acid, from the various carbohydrates of the 
 vegetable food — starch, sugar, &c. Much less oxygen 
 would be required to be eliminated from the nitro- 
 genous constituents, such as fibrine, &c, than from 
 a quantity of carbohydrate containing an equal 
 amount of carbon. The formation of fatty matter 
 in plants was of the same kind ; it was the result of 
 
22 THE SCIENTIFIC PRINCIPLES 
 
 a secondary action, starch being first formed from 
 carbonic acid and water. 
 
 Eef erring to the exercise of force, he argued that 
 the animal secretions must contain the products of 
 the metamorphosis of the tissues ; he concluded that 
 a starving man, with severe exertion, would secrete 
 more urea than the most highly fed individual in a 
 state of rest ; and he combated the idea that the 
 nitrogen of the food can pass into urea without 
 having previously become part of an organised tissue. 
 He said : — 
 
 'As an immediate effect of the manifestation of 
 mechanical force, we see that a part of the muscular 
 substance loses its vital properties, its character of 
 life ; that this portion separates from the living part, 
 and loses its capacity of growth and its power of 
 resistance. We find that this change of properties 
 is accompanied by the entrance of a foreign body 
 (oxygen) into the composition of the muscular fibre 
 * * * ; and all experience proves, that this conversion 
 of living muscular fibre into compounds destitute of 
 vitality is accelerated or retarded according to the 
 amount of force employed to produce motion. Nay, 
 it may safely be affirmed, that they are mutually 
 proportional ; that a rapid transformation of muscular 
 fibre, or, as it may be called, a rapid change of matter, 
 determines a greater amount of mechanical force ; 
 and conversely, that a greater amount of mechanical 
 motion (of mechanical force expended in motion) de- 
 termines a more rapid change of matter/ 
 
 Again : — 
 
 'The change of matter, the manifestation of 
 mechanical force, and the absorption of oxygen, are, 
 in the animal body, so closely connected with each 
 other, that we may consider the amount of motion, 
 
OF AGRICULTURE. 23 
 
 and the quantity of living tissue transformed, as 
 proportional to the quantity of oxygen inspired and 
 consumed in a given time by the animal.' 
 
 And again : — 
 
 ■ The production of heat and the change of matter 
 are closely related to each other ; but although heat 
 can be produced in the body without any change of 
 matter in living tissues, yet the change of matter 
 cannot be supposed to take place without the co- 
 operation of oxygen/ 
 
 Further, on the same point : — 
 
 ' The sum of force available for mechanical purposes 
 must be equal to the sum of the vital forces of all 
 tissues adapted to the change of matter.' 
 
 ' If, in equal times, unequal quantities of oxygen are 
 consumed, the result is obvious, in an unequal amount 
 of heat liberated, and of mechanical force.' 
 
 ' When unequal amounts of mechanical force are 
 expended this determines the absorption of corres- 
 ponding and unequal quantities of oxygen.' 
 
 Then, more definitely still, referring to the changes 
 which take place coincidently with the exercise of 
 force, and to the demands of the system for repair 
 accordingly, he says : — 
 
 1 The amount of azotised food necessary to restore 
 the equilibrium between waste and supply is directly 
 proportional to the amount of tissues metamorphosed.' 
 
 * The amount of living matter, which in the body 
 loses the condition of life, is, in equal temperatures, 
 directly proportional to the mechanical effects pro- 
 duced in a given time/ 
 
 s The amount of tissue metamorphosed in a given 
 time may be measured by the quantity of nitrogen 
 in the urine.' 
 
 ' The sum of the mechanical effects produced in 
 
24 THE SCIENTIFIC PRINCIPLES 
 
 two individuals, in the same temperature, is propor- 
 tional to the amount of nitrogen in their urine ; 
 whether the mechanical force has been employed in 
 voluntary or involuntary motions, whether it has been 
 consumed by the limbs or by the heart and other 
 viscera.' 
 
 Thus, apparently influenced by the physiological 
 considerations which he had adduced, and notwith- 
 standing that in some passages he seemed to recog- 
 nise a connection between the total quantity of 
 oxygen inspired and consumed, and the quantity of 
 mechanical force developed, Liebig nevertheless very 
 prominently insisted that the amount of muscular 
 tissue transformed — the amount of nitrogenous sub- 
 stance oxidated — was the measure of the force 
 generated. He accordingly draws the conclusion, 
 that the requirement for the nitrogenous constituents 
 of food will be increased in proportion to the increase 
 in the amount of force expended. 
 
 It will be obvious that the question whether, in 
 the feeding of animals for the exercise of mechanical 
 force, that is, for their labour, the demands of the 
 system will be proportionally the greater for the 
 nitrogenous, or for the non-nitrogenous constituents 
 of food, is one of considerable interest and practical 
 importance. 
 
 In reference to this point, to that of the sources 
 in the food of the fat of the animal body, as well 
 as to the requirements for the different constituents 
 of food for the maintenance, and for the general 
 increase, of the body, in the feeding of the animals of 
 the farm, a great deal of experimental evidence has 
 been acquired during the last forty years, both in this 
 country and on the Continent, and to this I shall 
 have to refer in some detail on a future occasion. 
 
OF AGRICULTURE. 25 
 
 So far, I have endeavoured to convey some idea 
 of the state of knowledge bearing upon the scientific 
 principles of agriculture, prior to the appearance of 
 Liebig's first two works on the subject; and also 
 briefly to summarise the views he then enunciated 
 in regard to some points of chief importance. I will 
 now attempt briefly to indicate what progress has 
 been made since that period, largely at any rate due 
 either to the direct influence of his teaching, or to 
 the stimulus given to enquiry by the discussions 
 which his writings called forth. 
 
 It is a coincidence of some interest, that the first 
 lectures given by the Sibthorpian Professor of Kural 
 Economy in this University, were delivered by my 
 predecessor, the late Dr. Daubeny, almost contem- 
 poraneously with the appearance of Liebig's first 
 Work, in 1840 ; one of a course of three having been 
 given before, and two within a few months after, the 
 publication of that work. These lectures were after- 
 wards published, and, in his preface, Professor Daubeny 
 expresses his indebtedness to Liebig's Work for some 
 of the fundamental doctrines, and for some of the 
 details embodied in his expositions. 
 
 In the lectures in question, Professor Daubeny 
 discussed the importance of the study of botany, 
 physiology, and chemistry, in the elucidation of agri- 
 cultural practices. He contrasted the conditions of 
 cultivation in the case of virgin soils, with those in 
 long-settled countries. He treated of the sources 
 of the constituents of our crops, of fallowing, manur- 
 ing, and rotation, so far as the knowledge of the 
 day permitted. 
 
 Finally, Dr. Daubeny put forward some specu- 
 lations as to the origin of the constituents of the 
 first vegetation on the surface of the globe, and 
 
26 THE SCIENTIFIC PRINCIPLES 
 
 especially as to the source of the combined carbon, 
 and the combined nitrogen, accumulated in the total 
 existing vegetable and animal life and remains. He 
 traced these to carbonic acid, and ammonia, evolved 
 by volcanic action. It may be observed that one 
 source of combined nitrogen is undoubtedly electrical 
 action, especially in equatorial regions, but it will 
 be seen further on, that so far as quantitative evi- 
 dence is at command on the point, the amounts of 
 combined nitrogen available from atmospheric sources 
 over a given area, within a given time, are, at any 
 rate in temperate latitudes, quite inadequate to ac- 
 count for the amounts recovered in crops over the 
 same area, and in the same time. It will be seen 
 too, that the question of the sources of the nitrogen 
 of our crops, is one upon which very conflicting views 
 are still entertained. 
 
 For a period of more than twenty-five years, 
 Dr. Daubeny continued to give lectures from time to 
 time on various branches of Eural Economy, generally 
 with some reference to the discussions of the day. 
 
 But independently of discourses of this expository 
 or critical kind, he, in 1845, described the results of 
 some experiments he had made to elucidate the prin- 
 ciples involved in the rotation of crops. To this 
 end he had set apart a number of plots in the 
 Botanic Garden, each 10 feet square. On some of 
 these he grew the same description of plant year 
 after year for several years in succession, whilst on 
 others he alternated the different crops. The soil 
 was admittedly not very favourable, being made 
 ground, and the plots were very small. Still the 
 results clearly showed that more produce was ob- 
 tained from a given area when the different plants 
 were grown in alternation, than when . the same 
 
OF AGRICULTURE. 27 
 
 description was grown successively. Subsequent 
 examination of the soils further showed considerable 
 differences, dependent on the exhaustion by the dif- 
 ferent crops. 
 
 Dr. Daubeny confined his illustrations and his dis- 
 cussions almost entirely to the mineral or ash-con- 
 stituents of the crops; thus following the lines of 
 argument current at the time. Although the facts 
 brought out are of interest, all subsequently acquired 
 evidence tends to show, that the benefits of rotation 
 are not explicable by exclusive reference to the dif- 
 ference in the description, and amounts, of the mineral 
 constituents which are taken up by the different crops. 
 
 Among the most notable of Professor Daubeny' s 
 lectures, was a course of eight on Koman Husbandry, 
 which were afterwards published. 
 
 These lectures evince considerable historical re- 
 search, and are of much interest independently of 
 the facts relating to the Agriculture of the Ancients 
 which they bring to light. But their chief interest 
 to the agricultural student of the present day is to 
 be found in the evidence, discernible between the 
 lines, that certain practices then adopted for the 
 increase of the products obtained from the land, 
 are still recognised as effective, though, in some cases, 
 the precise explanation of the benefits derived yet 
 remains a matter of controversy. Thus, although no 
 fixed rotations of crops seem to have been adopted, 
 yet the occasional growth of plants of the Legu- 
 minous family was had recourse to, and recognised as 
 a means of increasing the growth of the gramineous 
 crops with which they were alternated. 
 
 Again, the evidence of both Columella and Virgil 
 goes to show, that the fertility of soils was then 
 attributed to the accumulations from previous natural 
 
28 THE SCIENTIFIC PRINCIPLES 
 
 vegetation, and that, as this store was gradually used 
 up, the soils became poor. 
 
 Although, as has been said, the lectures which 
 have been given by the Sibthorpian Professor of Rural 
 Economy commenced almost simultaneously with the 
 appearance of Liebig's first work, and many of them 
 had direct reference either to Liebig's own views, 
 or to current discussions relating to them, their in- 
 auguration was prior to, and quite independent of, 
 the interest excited by that work. Not so was it, in 
 the case of many other agencies for promoting know- 
 ledge in regard to the scientific principles of agri- 
 culture, both in this country, and on the Continents 
 of Europe and America. I think too, I may safely 
 say, that the stimulus was earlier felt, and was 
 earlier productive of results, in this country, than in 
 Liebig's own, or elsewhere. 
 
 In 1843, the Royal Agricultural Society of England 
 first appointed a consulting Chemist ; Dr., now Sir 
 Lyon Play fair, being the first holder of the office. 
 In 1848, the late Professor Way was elected, and 
 the Society's journals of that time bear testimony 
 to his clear perception of the agricultural problems re- 
 quiring solution, and of his capacity as an investigator. 
 In 1858, Dr. Voelcker succeeded to the office, and 
 continues to hold it with much advantage to that 
 union of f Practice with Science/ which the Society 
 by its motto recognises as so essential to progress. 
 Thus, after having been Professor of Chemistry at 
 the Royal Agricultural College, Cirencester, for many 
 years, Dr. Voelcker has now been consulting Chemist 
 to the Royal Agricultural Society of England for 
 more than a quarter of a century ; and to some of 
 the results of his investigations I shall have to refer 
 on future occasions. 
 
OF AGRICULTURE. 29 
 
 It was also in 1843, that there was established the 
 Chemico-Agricultural Society of Scotland, which was, 
 I believe, broken up after it had existed between 
 four and five years, because its able Chemist, the late 
 Professor Johnston, failed to find a remedy for the 
 potato disease. Somewhat similar duties, including 
 a good deal of agricultural research, have however 
 since been performed under the auspices of the High- 
 land and Agricultural Society of Scotland, for many 
 years by the late Professor Anderson, and more 
 recently by Dr. Aitken. 
 
 In 1845, the Chemico-Agricultural Society of 
 Ulster was established ; Professor Hodges was ap- 
 pointed as Chemist, and he continues ably to perform 
 the duties of the office. 
 
 As already intimated, agencies of this kind were 
 not so soon brought into operation on the Continent. 
 Nevertheless, the numerous Agricultural Experi- 
 mental Stations which have been established, not 
 only in Germany, but in most continental States, 
 owe their origin very directly to the writings, the 
 teachings, and the influence of Liebig. 
 
 The movement seems to have originated in Saxony, 
 where Stockhardt had already stimulated interest in 
 the subject by his lectures and his writings. After 
 some correspondence in 1850-51, between the late 
 Dr. Crucius and others on the one side, and the 
 Government on the other, the first so-called 'Agri- 
 cultural Experimental Station' was established at 
 Mochern, near Leipzig, in 185 1-2. In 1877 the 
 twenty-fifth anniversary of the foundation of that In- 
 stitution was celebrated at Leipzig ; when an account, 
 which has since been published, was given of the 
 number of Stations then existing, of the number of 
 Chemists engaged, and of the subjects which had 
 
30 
 
 THE SCIENTIFIC PRINCIPLES 
 
 been investigated. From that statement we learn 
 that at that period the number of Stations was : — 
 
 In the various German States 
 
 In Austria 
 
 In Italy 
 
 In Sweden 
 
 In Denmark 
 
 In Russia 
 
 In Belgium 
 
 In Holland 
 
 In France 
 
 In Switzerland 
 
 In Spain 
 
 Total 
 
 74 
 16 
 10 
 
 7 
 i 
 
 3 
 3 
 
 2 
 2 
 
 3 
 
 i 
 
 122 
 
 Thus, seven years ago there were 122 'Agricultural 
 Stations ' on the Continent of Europe, and the num- 
 ber has doubtless by this time considerably increased. 
 
 Each of these Stations is under the direction of a 
 Chemist, frequently with one or more assistants. 
 One special duty of most of them is to examine or 
 analyse, and report upon, manures, seeds, or feeding- 
 stuffs, offered for sale to the farmer ; and it seems to 
 have been found to be the interest of the dealers in such 
 commodities, to submit their proceedings to a certain 
 degree of supervision by the Chemist of the Station 
 of their District. 
 
 But agricultural research has also been a character- 
 istic feature of these institutions. It was stated in 
 the report referred to, that the investigation of soils 
 had been the prominent object at sixteen of them ; 
 experiments with manures at twenty-four ; vegetable 
 physiology at twenty-eight ; animal physiology and 
 feeding experiments at twenty ; vine culture and 
 wine making at thirteen ; forest culture at nine ; and 
 milk production at eleven. Others, according to their 
 locality, have devoted special attention to fruit 
 culture, olive culture, the treatment of moor, bog and 
 
OF AGRICULTURE. 31 
 
 peat land, the production of silk, the manufacture of 
 spirit, and other products. 
 
 But few experimental stations having in the main 
 similar objects to those of the Stations on the Conti- 
 nent of Europe, have been established either in our 
 own Country or in America ; but in the German 
 Report above cited, Scotland is credited with one, and 
 the United States with one. 
 
 There are, however, several Stations in the United 
 States, where agricultural investigation is carried on ; 
 and a writer in that Country has recently made an 
 appeal to the Government, to establish Stations 
 with a view to the investigation of each general 
 variety of soil and climate in the United States ; to 
 assign a Chemist to each, to institute experiments 
 with the crops most suitable to the locality, to analyse 
 the soil, &c, and to report the results. 
 
 The records of the results of the investigations con- 
 ducted at the large number of experimental stations on 
 the Continent of Europe, are extremely voluminous ; 
 and the number of systematic works which have ap- 
 peared on various branches of the subject in the 
 French and German languages during the last forty 
 years is very great. I will here refer to the several 
 editions of Liebig's first two works already alluded 
 to, his ' Familiar Letters on Chemistry,' his ' Modern 
 Agriculture/ his 'Principles,' and finally his * Natural 
 Laws of Husbandry,' all of which have appeared in 
 the English language. Reference should also be 
 made to Boussingault's 'Econornie Rurale' the first 
 edition of which was published in English in 1845. 
 It has, however, gone through other editions in 
 France ; and subsequently, at intervals from 1 860 
 to 1878, Boussingault published a series of six 
 volumes, entitled — ' Agronomie, Chimie Agricole et 
 
32 THE SCIENTIFIC PRINCIPLES. 
 
 Physiologie' — and covering a still wider range of 
 subjects, bringing the information on the various 
 points up to date, and going into much detail as to the 
 methods of research, as well as to the results obtained. 
 In these volumes, those who desire it will be able to 
 examine for themselves the evidence upon which many 
 important conclusions have been based. 
 
 A few of the works by English authors which have 
 appeared within the same period, it may be well to 
 enumerate. Among them are Johnston's * Lectures on 
 Agricultural Chemistry and Geology/ first published 
 in 1844; and his 'Experimental Agriculture/ pub- 
 lished in 1849. His successor, Dr. Anderson, also 
 published, in i860, a work entitled — 'Elements of 
 Agricultural Chemistry/ 
 
 New editions of Johnston's work have since been 
 published by Dr. C. Cameron ; the first of these, the 
 tenth of the original work, appearing in 1877. 
 
 Perhaps the most compendious record of the results 
 of the Continental investigations up to the time 
 of its publication, which has appeared in our own 
 language, is that by Professor S. W. Johnson, of Yale 
 College, Newhaven, Connecticut, in two volumes, 
 entitled ' How Crops Grow/ and ' How Crops Feed/ 
 The results of the German experiments on the 
 Feeding of Animals have also been summarised by 
 Dr. Armsby, in a volume published in America, and 
 entitled — ' Manual of Cattle-Feeding/ 
 
 Neither in the works above referred to, nor in the 
 reports of the Continental Experimental Stations, do 
 we find the record of many systematic or long con- 
 tinued field-experiments. We have, however, the 
 example of Boussingault, and the opinions of Sir 
 Humphrey Davy, Liebig, and Daubeny, as to the great 
 importance of such methods of agricultural research. 
 
OF AGRICULTURE. 33 
 
 Davy says : — 
 
 1 Nothing is more wanting in agriculture than ex- 
 periments in which all the circumstances are minutely 
 and scientifically detailed. This art will advance 
 with rapidity in proportion as it becomes exact in its 
 methods. As in physical researches, all the causes 
 should be considered ; a difference in the results may 
 be produced, even by the fall of a half-inch of rain 
 more or less in the course of a season, or a few degrees 
 of temperature, or even by a slight difference in the 
 subsoil, or in the inclination of the land.' 
 
 * Information collected after views of distinct in- 
 quiry, would necessarily be fitted for inductive reason- 
 ing, and capable of being connected with the general 
 principles of science ; and a few histories of the re- 
 sults of truly philosophical experiments in agricultural 
 chemistry would be of more value in enlightening and 
 benefiting the farmer, than the greatest possible accu- 
 mulation of imperfect trials, conducted merely in the 
 empirical spirit.' 
 
 1 It is from the higher classes of the community, 
 from the proprietors of land, — those who are fitted by 
 their education, to form enlightened plans, and by 
 their fortunes, to carry such plans into execution ; it 
 is from these that the principles of improvement must 
 flow to the labouring classes of the community ; and 
 in all classes the benefit is mutual ; for the interest of 
 the tenantry must be always likewise the interest of 
 the proprietors of the soil.' 
 
 * Discoveries made in the cultivation of the earth 
 are not merely for the time and country in which they 
 are developed, but they may be considered as extend- 
 ing to future ages, and as ultimately tending to benefit 
 the whole human race ; as affording subsistence for 
 generations yet to come ; as multiplying life ; and not 
 
 D 
 
34 THE SCIENTIFIC PRINCIPLES 
 
 only multiplying life, but likewise providing for its 
 enjoyment/ 
 
 Liebig said : — * I shall be happy if I succeed in 
 attracting the attention of men of science to subjects 
 which so well merit to engage their talents and 
 energies. Perfect agriculture is the true foundation 
 of all trade and industry — it is the foundation of 
 the riches of states. But a rational system of agri- 
 culture cannot be formed without the application of 
 scientific principles ; for such a system must be based 
 on an exact acquaintance with the means of nutri- 
 tion of vegetables, and with the influence of soils and 
 actions of manure upon them. This knowledge we 
 must seek from chemistry, which teaches the mode 
 of investigating the composition and of studying the 
 characters of the different substances from which 
 plants derive their nourishment.' 
 
 * Since the time of the immortal author of the 
 "Agricultural Chemistry" (Davy) no chemist has oc- 
 cupied himself in studying the application of chemical 
 principles to the growth of vegetables, and to organic 
 processes. I have endeavoured to follow the path 
 marked out by Sir Humphrey Davy, who based his 
 conclusions only on that which was capable of in- 
 quiry and proof. This is the path of true philo- 
 sophical inquiry, which promises to lead us to truth 
 — the proper object of our research.' 
 
 The importance which Professor Daubeny attached 
 to field-experiments, is evidenced in the facts that, at 
 a very early period of his connection with the study 
 and teaching of the principles of Rural Economy, he 
 instituted the experiments on Rotation, in the Botanic 
 Garden, already referred to ; and that subsequently, 
 I believe in i860, he bequeathed to his successors 
 in the Chair a piece of ground of about one and a 
 
OF AGRICULTURE. 35 
 
 half acre for the purposes of experiments ; feeling, as 
 he said in a lecture on the subject, that the objects 
 of the foundation of the Professorship of Rural 
 Economy — * would not be fully attained until the 
 holder of it was enabled, not only to retail the in- 
 formation he might obtain from books, but also to 
 illustrate it by experiment, and to verify, as well 
 as extend the knowledge he might have derived from 
 others through original investigations of his own.' 
 
 Briefly described, the subjects which Dr. Daubeny 
 indicated as suitable for such enquiry were — i. To 
 determine what amount of mechanical treatment, and 
 what length of time, would be required to bring an 
 exhausted soil back to fertility without manure. 
 2. To try whether, if a soil be rich in mineral con- 
 stituents, ammoniacal manures may not be dispensed 
 with by the use of mechanical operations; since, as 
 he says, Liebig's. opinion is, that many plants have 
 the power ' of absorbing from the atmosphere so 
 large an amount of ammonia, as would seem to 
 render them independent of animal manures, and to 
 enable them to derive all their ingredients, except 
 their mineral ones, from the atmosphere.' 3. The 
 causes of the failure of clover. 4. The effects of 
 gypsum applied as manure. 5. To try whether there 
 is any disadvantage in the use of superphosphates 
 from which the fluorine has been dissipated, com- 
 pared with bones from which it has not. 6. Whether 
 growing plants year after year on the same land 
 from the seed yielded, tends to variation, or to the 
 obliteration of specific characters. 7. Lastly, to de- 
 termine how far the growth of the fungi which 
 attack different crops may be considered as a cause, 
 or only the effect, of disease. 
 
 I may here say that much experimental evidence 
 
 D 1 
 
36 THE SCIENTIFIC PRINCIPLES 
 
 is now available with regard to some of these ques- 
 tions, and I shall have to call attention to it in 
 subsequent lectures. 
 
 I may add that, very shortly after Dr. Daubeny 
 had bequeathed the piece of ground to which I have 
 referred, I visited it with him, and at the time ex- 
 pressed a fear that it was not very suitable for the 
 objects in view, little thinking that it would fall to 
 my lot to consider the subject more seriously, as 
 I shall soon have to do. In the first place, I pointed 
 out the unlevel character of the plot, and gathered 
 from the history of it given to me, that it was very 
 uneven as to condition. Accordingly, I suggested 
 that, before any experiments on it were undertaken, 
 it should be brought into an even state as far as 
 mechanical operations could accomplish this ; and 
 that then some corn-crop should be grown for several 
 years in succession without manure, so as, as far as pos- 
 sible, to obliterate the unevenness of condition arising 
 from previous irregularity in manuring and cropping. 
 
 It will doubtless excite surprise when I say that, 
 notwithstanding the importance of the subject, and the 
 high authority on which the prosecution of scientific- 
 ally conducted field-experiments has been advocated, 
 the conduct of such experiments has never been an 
 important part of the work of the Agricultural Experi- 
 mental Stations on the continent of Europe, and that 
 it is now almost excluded from their programme. 
 
 In 1880, Professor Maercker of Halle, one of the 
 leading Agricultural Chemists of Germany, stated that 
 belief in their value was greatly diminished, and that 
 by some they were declared to be of no value. It is 
 objected that the Chemists of the Agricultural Stations 
 have neither the means nor the technical know- 
 ledge necessary for carrying out such experiments 
 
OF AGRICULTURE. 37 
 
 successfully; that neither the amount of land, nor the 
 funds at their disposal, are such as to admit of any- 
 safe deductions for application in practical agricul- 
 ture from the results ; and that purely physiological 
 problems can be better investigated in the laboratory, 
 or in the greenhouse. He remarks that, owing to the 
 errors necessarily incident to field-experiments con- 
 ducted by those not acquainted with practical agri- 
 culture, the confidence of the practical farmer in the 
 results has been shaken. Indeed, owing to the diffi- 
 culties and cost of such enquiries, if conducted in a 
 truly scientific manner, so as to be applicable for the 
 solution of questions of fundamental and general 
 interest, Professor Maercker concludes that the only 
 field-experiments which it is practicable to carry out 
 in Germany, are such as should be conducted by the 
 practical farmer himself, to test the applicability to 
 practice, of results and conclusions otherwise arrived 
 at; and that, to insure that even such experiments 
 are not misleading, similar ones should be conducted 
 on different descriptions of soil, and for several years 
 in succession. 
 
 I have already quoted the opinion of Sir Humphrey 
 Davy, that scientifically conducted field-experiments 
 should be undertaken by proprietors of land, who by 
 their education are fitted to form enlightened plans, 
 and by their fortunes are able to carry them into 
 execution ; and when I tell you that the Kothamsted 
 field-experiments, independently of all the laboratory 
 investigations connected with them, cost considerably 
 more, and those which have been undertaken by the 
 Duke of Bedford at Woburn for the last seven years, 
 on behalf of the Koyal Agricultural Society of Eng- 
 land, and which are under the direction of Dr. 
 Voelcker, not much less, than £1000 annually, you 
 
38 THE SCIENTIFIC PRINCIPLES 
 
 will not be surprised that such field-experiments are 
 not more general. 
 
 Prior to the appearance of Liebig's first work, in 
 1840, Mr., now Sir John Bennet Lawes, commenced 
 experiments with different manuring substances, first 
 with plants in pots, and afterwards in the field, at 
 Rothamsted, into the hereditary possession of which 
 he had entered on his majority in 1834. The results 
 so obtained on a small scale in 1837, J ^3^» an( ^ l &39> 
 were such as to lead to more extensive trials in the 
 field in 1840, 1841, and subsequently. 
 
 In 1843, more systematic field-experiments were 
 commenced; and a barn, which had already been 
 applied to laboratory purposes, became almost ex- 
 clusively devoted to agricultural investigations. 
 These, which are still in progress, have been con- 
 ducted entirely at the cost of Sir John Lawes, who 
 has further set apart a sum of £100,000, and certain 
 areas of land, for their continuance after his death. 
 
 In June 1843, I became associated with Mr. Lawes 
 in the conduct of these investigations; and as it is 
 doubtless my connexion with them (which still con- 
 tinues), to which my election to this Chair is mainly 
 to be attributed, it will not be out of place to give, 
 on this occasion, a brief outline of the scope and plan 
 of the work which has been accomplished, during the 
 more than forty years of its continuance. That I 
 should do so seems the more desirable, since I inter- 
 pret my appointment as indicating a feeling on the 
 part of the Electors, that the results acquired in this 
 long period of investigation of the scientific principles 
 of agriculture, many of which are known by their 
 publication, must have provided important material 
 for illustration, in the lectures which it will be my 
 
OF AGRICULTURE. 39 
 
 duty to deliver. In fact, whilst I shall not neglect 
 important results and conclusions established by 
 others, the plan which I have in view will never- 
 theless involve much reliance on the data acquired 
 at Rothamsted. 
 
 I may premise that since July 1855, when a new 
 laboratory, built by public subscription of agricul- 
 turists, was presented to Mr. Lawes, the old barn 
 laboratory has been abandoned. At the present 
 time, the Rothamsted staff consists of two, and some- 
 times three chemists; several general assistants in 
 different departments ; occasionally a botanical assist- 
 ant ; three, and sometimes four, computors and record 
 keepers; also a laboratory man, and several boys. 
 
 The general scope and plan of the field-experiments 
 has been — to grow some of the most important crops 
 of rotation, each separately, year after year, for many 
 years in succession on the same land, without manure, 
 with farmyard manure, and with a great variety of 
 chemical manures ; the same description of manure 
 being, as a rule, applied year after year on the same 
 plot. Experiments, with different manures on the 
 mixed herbage of permanent grass-land, on the effects 
 of fallow, and on an actual course of rotation, without 
 manure, and with different manures, have likewise 
 been made. 
 
 Field-experiments have thus been conducted for 
 the periods, and over the areas, indicated in the 
 table on the following page. 
 
 Samples of all the experimental crops are brought 
 to the laboratory. Weighed portions of each are 
 partially dried and preserved for future reference, or 
 analysis. Duplicate weighed portions of each are 
 dried at ioo°C, the dry matter determined, and then 
 burnt to ash. The quantities of ash are determined 
 
40 
 
 THE SCIENTIFIC PRINCIPLES 
 
 Rothamsted Field Experiments. 
 
 Crops. 
 
 Duration. 
 
 Area. 
 
 Plots. 
 
 
 Years. 
 
 Acres. 
 
 
 Wheat (various manures) . 
 
 41 
 
 13 
 
 37 
 
 Wheat, alternated with Fallow 
 
 33 
 
 1 
 
 2 
 
 Wheat (varieties) .... 
 
 15 
 
 4-8 
 
 about 20 
 
 Barley (various manures) 
 
 33 
 
 4i 
 
 29 
 
 Oats (various manures) . . 
 
 IO 1 
 
 3 
 
 4 
 
 6 
 
 Beans (various manures) 
 
 32 2 
 
 1} 
 
 10 
 
 Beans (various manures) 
 
 2 7 3 
 
 I 
 
 5 
 
 Beans, alternated with Wheat 
 
 28* 
 
 I 
 
 10 
 
 Clover (various manures) . 
 
 30 5 
 
 3 
 
 18 
 
 Various Leguminous Plants 
 
 7 
 
 3 
 
 17 
 
 Turnips (various manures) . 
 
 23 6 
 
 8 
 
 40 
 
 Sugar Beet (various manures) 
 
 5 
 
 8 
 
 41 
 
 Mangel- Wurzel (various manur 
 
 3s). 9 
 
 8 
 
 41 
 
 Total Root Crops 
 
 42 
 
 
 
 Potatoes (various manures) . 
 
 9 
 
 2 
 
 10 
 
 Rotation (various manures) 
 
 37 
 
 2\ 
 
 12 
 
 Permanent Grass (various manu 
 
 res) 29 
 
 7 
 
 22 
 
 and recorded ; the ashes themselves being preserved 
 for reference, or analysis. 
 
 In a large proportion of the samples the total 
 nitrogen is determined; and in some the amount 
 existing as albuminoids, amides, and nitric acid. 
 
 In selected cases, illustrating the influence of season, 
 manures, exhaustion, &c, complete ash-analyses have 
 been made, numbering in all more than 700. 
 
 Also in selected cases, illustrating the influence 
 of season and manuring, quantities of the experi- 
 
 1 Including i year Fallow. 
 
 2 Including I year Wheat, and 5 years Fallow. 
 
 3 Including 4 years Fallow. 
 
 4 Including 2 years Fallow. 
 
 5 Clover, 1 2 times sown, 8 yielding crops, but 4 of these very small, 1 year 
 Wheat, 5 years Barley, 1 2 years Fallow. 
 
 6 Including Barley without manure 3 years (nth, 12th, and 13th seasons). 
 
OF AGRICULTURE. 41 
 
 mentally grown wheat- grain have been sent to the 
 mill, and the proportion and composition of the 
 different mill-products has been determined. 
 
 In the sugar-beet, mangel-wurzel, and potatoes, 
 the sugar in the juice has in many cases been de- 
 termined by polariscope, and frequently by copper 
 also. 
 
 In the case of the experiments on the mixed 
 herbage of permanent grass-land, besides the samples 
 taken for the determination of the chemical com- 
 position (dry matter, ash, nitrogen, woody fibre, 
 fatty matter, and composition of ash), carefully 
 averaged samples have frequently been taken for 
 the determination of the botanical composition. In 
 this way, on four occasions, at intervals of five years 
 — viz., in 1862, 1867, ^72, and 1877 — a sample of 
 the produce of each plot was taken, and submitted 
 to careful botanical separation ; and the percentage, 
 by weight, of each species in the mixed herbage 
 determined. Partial separations, in the case of 
 samples from selected plots (frequently of both first 
 and second crops), have also been made in other years. 
 
 Samples of the soils of most of the experimental 
 plots have been taken from time to time, generally 
 to the depth of 9, 18, and 27 inches; sometimes to 
 twice, and sometimes even to four times this depth. 
 In this way more than 1000 samples have been 
 taken, submitted to partial mechanical separation, 
 and portions of the fine soil (that is, excluding 
 stones) have been carefully prepared and preserved 
 for analysis. In a large proportion of the samples 
 the loss on drying at different temperatures, and at 
 ignition, has been determined. In most, the nitrogen 
 determinable by burning with soda-lime has been 
 estimated. In many the carbon, and in some the 
 
42 THE SCIENTIFIC PRINCIPLES 
 
 nitrogen as nitric acid, and the chlorine, have been 
 determined. Some experiments have also been made 
 on the comparative absorptive capacity (for water 
 and ammonia) of different soils and subsoils. The 
 systematic investigation of the amount, and the 
 condition, of the nitrogen, and of some of the more 
 important mineral constituents, of the soils of the 
 different plots, and from different depths, is now in 
 progress, or contemplated. 
 
 Almost from the commencement of the experi- 
 ments the rainfall has been measured — for more than 
 thirty years in a gauge of one-thousandth of an acre 
 area, as well as in an ordinary small funnel-gauge of 
 5 inches diameter. An 8-inch ' Board of Trade ' 
 copper-gauge is also now in use, commencing 
 January i, 1881. From time to time, the nitrogen 
 as ammonia (and sometimes as nitric acid), has been 
 determined in the rain waters. The chlorine has also 
 been determined in many samples. 
 
 Three ' drain gauges/ also of one-thousandth of an 
 acre each, for the determination of the quantity and 
 composition of the water percolating, respectively 
 through 20 inches, 40 inches, and 60 inches depth of 
 soil (with its subsoil in natural state of consolidation), 
 have also been constructed. Each of the differently 
 manured plots of the permanent experimental wheat- 
 field having a separate pipe-drain, the drainage- 
 waters have been, and are frequently, collected and 
 analysed. 
 
 The nitrogen existing as nitric acid, sometimes 
 that in other forms, and also some other constituents, 
 are, and for some time past have been, determined 
 periodically, in both the rain and the various drainage 
 waters. 
 
 For several years in succession, experiments were 
 
OF AGRICULTURE. 43 
 
 made to determine the amount of water given off by 
 plants during their growth. In this way various 
 plants, including representatives of the gramineous, 
 the leguminous, and other families, have been ex- 
 perimented upon. Similar experiments have also 
 been made with various evergreen and deciduous 
 trees. 
 
 Having regard to the difference in the character 
 and amount of the constituents assimilated by plants 
 of different botanical relationships, under equal ex- 
 ternal conditions, or by the same description of 
 plants, under varying conditions, observations have 
 been made on the character and range of the roots of 
 different plants, and on their relative development of 
 stem, leaf, &c. In the case of various crops, but 
 more especially with wheat and beans, samples have 
 been taken at different stages of growth, and the 
 composition determined, in more or less detail, some- 
 times of the entire plant, and sometimes of the 
 separated parts. In a few cases, the amounts of dry 
 matter, ash, nitrogen, &c, in the above-ground 
 growth of a given area, at different stages of 
 development, have been determined. The amounts 
 of stubble of different crops have also occasionally 
 been estimated. 
 
 Experiments were made for several years in 
 succession to determine whether plants assimilated 
 free or uncombined nitrogen, and also various col- 
 lateral points. Plants of the gramineous, the 
 leguminous, and of other families, were operated 
 upon. The late Dr. Pugh took a prominent part 
 in this enquiry. 
 
 Obviously, an investigation of the scientific prin- 
 ciples of Agriculture would be incomplete if it were 
 
44 THE SCIENTIFIC PRINCIPLES 
 
 not extended to the question of the feeding of the 
 animals of the farm. Accordingly, experiments with 
 such animals were commenced early in 1847, an d 
 have been continued at intervals up to the present 
 time. 
 
 The following points have been investigated : — 
 
 1. The amount of food, and of its several con- 
 stituents, consumed in relation to a given live-weight 
 of animal, within a given time. 
 
 2. The amount of food, and of its several con- 
 stituents, consumed to produce a given amount of 
 increase in live-weight. 
 
 3. The proportion, and relative development, of 
 the different organs or parts of different animals. 
 
 4. The proximate and ultimate composition of the 
 animals, in different conditions as to age and fatness, 
 and the probable composition of their increase in 
 live- weight during the fattening process. 
 
 5. The composition of the solid and liquid excreta 
 (the manure), in relation to that of the food con- 
 sumed. 
 
 6. The loss or expenditure of constituents by 
 respiration and the cutaneous exhalations — that is, 
 in the mere sustenance of the living meat — and 
 — manure-making machine. 
 
 Several hundred animals — oxen, sheep, and pigs — 
 have been submitted to experiment. 
 
 The amount, and the relative development, of the 
 different organs and parts, were determined in two 
 calves, two heifers, fourteen bullocks, one lamb, 249 
 sheep, and 59 pigs. 
 
 The percentages of water, mineral matter, fat, and 
 nitrogenous substance, were determined in certain 
 separated parts, and in the entire bodies, of ten 
 animals — namely, one calf, two oxen, one lamb, four 
 
OF AGRICULTURE. 45 
 
 sheep, and two pigs. Complete analyses of the ashes, 
 respectively, of the entire carcases, of the mixed 
 internal and other ' offal ' parts, and of the entire 
 bodies, of each of these ten animals have also been 
 made. 
 
 From the data provided, as just described, as to 
 the chemical composition of the different descriptions 
 of animal, in different conditions as to age and fatness, 
 the composition of the increase whilst fattening, and 
 the relation of the constituents stored up in increase 
 to those consumed in food, have been estimated. 
 
 To ascertain the composition of the manure in 
 relation to that of the food consumed, oxen, sheep, 
 and pigs, have been experimented upon. 
 
 The loss or expenditure of constituents, by respir- 
 ation and the cutaneous exhalations, has not been 
 determined directly, but only by difference ; that is, 
 by calculation, founded on the amounts of dry matter, 
 ash, nitrogen, &c, in the food, and in the (increase) 
 faeces, and urine. 
 
 Independently of the points of enquiry here enu- 
 merated, the results obtained have supplied data for 
 the consideration of the following questions : — 
 
 i. The characteristic demands of the animal body, 
 for nitrogenous or non-nitrogenous constituents of 
 food, in the exercise of muscular power. 
 
 2. The sources in the food of the fat produced in 
 the animal body. 
 
 3. The comparative characters of animal and veg- 
 etable food in human dietaries. 
 
 Supplementary investigations have also been made ; 
 for example — on the application of town-sewage to 
 different crops, including experiments on the feed- 
 ing qualities of the produce grown ; the amount of 
 increase yielded by oxen, and the amount and com- 
 
46 THE SCIENTIFIC PRINCIPLES 
 
 position of the milk yielded by cows, being deter- 
 mined. 
 
 The chemistry of the malting process, the loss of 
 food constituents during its progress, and the com- 
 parative feeding value of barley and malt, have also 
 been investigated. 
 
 Many of the results of the investigations above 
 enumerated have already been published, but a large 
 proportion as yet remains unpublished. 
 
 As already intimated, I propose to rely largely on 
 the data supplied in the more than forty years of 
 investigation at Eothamsted ; in the field, the feeding- 
 shed, and the laboratory, in the lectures which it 
 will be my duty to give in this University, in elu- 
 cidation of the scientific principles of agriculture. 
 
 In the first place, however, to give logical sequence 
 to what will follow, I shall devote a few lectures to 
 the question of the sources of the constituents of the 
 plants and animals which are the products of the 
 art of agriculture. Obviously, the soil, and the atmo- 
 sphere, are these sources. The subject of the origin, 
 the general characters, and the composition, of soils, 
 is a very wide one ; and many lectures might be 
 devoted to its discussion. But it is foreign to my 
 plan so to discuss it ; as to do so would seriously 
 trench upon the time which should be devoted to 
 the consideration of other branches of our enquiry. 
 
 I shall next consider the effects of manures, ex- 
 haustion, and variations of season, on the amounts 
 of produce, and on the composition of the produce, 
 of different crops, the effects of fallow, and the 
 benefits arising from a rotation of crops. 
 
 Subsequently, I propose to take up the subject 
 of the feeding of animals, for the production of meat, 
 
OF AGRICULTURE. 47 
 
 milk, and manure, and for the exercise of force — that 
 is, for their labour. Also, if opportunity should 
 occur, to treat of the question of the application of 
 town-sewage to the land. 
 
 Finally, I should observe that, throughout the 
 illustrations which I shall bring before you, it will 
 be my endeavour to keep in view the bearing of the 
 data with which I shall have to deal, on the im- 
 portant question of compensation for unexhausted 
 improvements, so much in discussion at the present 
 time. 
 
 The first experiments on crops to which I shall 
 direct attention, will be those on the cereals ; for, 
 although bad seasons, and foreign competition, have 
 of late tended to lessen the relative importance of 
 these products to the British farmer, the experimental 
 evidence obtained, both in the field and in the labora- 
 tory, is more complete in regard to them than to any 
 other crops ; and the discussion of the results, will 
 afford the opportunity of considering important ques- 
 tions of wider interest to agriculture, than those 
 exclusively relating to the production of the cereal 
 crops themselves. 
 
 Printed at the University Press, Oxford 
 
 By Horace Hart, Printer to the University 
 

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