Humphry Davy, Poet and Philosopher

by T. E. Thorpe

It would be impossible in the space at our disposal to attempt to give a minute analysis of Davy’s work in connection with agriculture. Its interest now is, for the most part, historical; what is of permanent importance in the way of fact has long since been woven into the common web of knowledge. Its greatest value was not in the novelty or the abundance of its facts, but rather as a closely-reasoned exposition of the relation of agriculture to science, and of the necessity for applying the principles and methods of science to the art. The philosophic breadth of his views, supported, on occasion, by apt example and striking analogy, might be illustrated by many extracts. This, for example, is how he speaks of the value of the scientific method, and of chemistry, to husbandry:—

“Nothing is more wanting in agriculture than experiments, 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 an 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 inquiry, would necessarily be more accurate, and more capable of being connected with the general principles of science; and a few histories of the results of truly philosophical experiments in agricultural chemistry would be of more value in enlightening and benefitting the farmer, than the greatest possible accumulation of imperfect trials conducted merely in the empirical spirit. It is no unusual occurrence, for persons who argue in favour of practice and experience, to condemn generally all attempts to improve agriculture by philosophical inquiries and chemical methods. That much vague speculation may be found in the works of those who have lightly taken up agricultural chemistry, it is impossible to deny. It is not uncommon to find a number of changes rung upon a string of technical terms, such as oxygen, hydrogen, carbon, and azote, as if the science depended upon words rather than upon things. But this is, in fact, an argument for the necessity of the establishment of just principles of chemistry on the subject. Whoever reasons upon agriculture, is obliged to recur to this science. He feels that it is scarcely possible to advance a step without it; and if he is satisfied with insufficient views, it is not because he prefers them to accurate knowledge, but, generally, because they are more current.... It has been said, and undoubtedly with great truth, that a philosophical chemist would most probably make a very unprofitable business of farming; and this certainly would be the case, if he were a mere philosophical chemist; and unless he had served his apprenticeship to the practice of the art, as well as to the theory. But there is reason to believe that he would be a more successful agriculturist than a person equally uninitiated in farming, but ignorant of chemistry altogether; his science, as far as it went, would be useful to him. But chemistry is not the only kind of knowledge required: it forms a part of the philosophical basis of agriculture; but it is an important part, and whenever applied in a proper manner must produce advantages.”

How highly these lectures were appreciated will be evident from the terms in which they were referred to by Sir John Sinclair in his address of 1806 to the Board. He says:—

“In the year 1802, when my Lord Carrington was in the chair, the Board resolved to direct the attention of a celebrated lecturer, Mr. Davy, to agricultural subjects; and in the following year, during the presidency of Lord Sheffield, he first delivered to the members of this Institution, a course of lectures on the Chemistry of Agriculture. The plan has succeeded to the extent which might have been expected from the abilities of the gentleman engaged to carry it into effect. The lectures have hitherto been exclusively addressed to the members of the Board; but to such a degree of perfection have they arrived, that it is well worthy of consideration, whether they ought not to be given to a larger audience.”

The “degree of perfection” was in no small degree due to the amount of experimental and observational work which Davy introduced into his lectures. Mr. Bernard allotted him a considerable piece of ground on his property at Roehampton for experimental purposes, and the Duke of Bedford carried out trials for him at Woburn. He studied from time to time all the operations of practical farming, examined a great variety of soils, and investigated the nature and action of manures. He was thus brought into contact with some of the largest landowners and agriculturists of his time, and was an honoured guest in the houses of men like Lord Sheffield, Lord Thanet, Mr. Coke of Holkham, and others.[E] In the practical interest he thus displayed in the most useful of all the arts he sought to emulate the example of his illustrious prototype Lavoisier, and his work constitutes the foundation of every treatise on the subject since the appearance, in 1840, of Liebig’s well-known book.

[E] In the print of the “Woburn Sheep-Shearing,” Davy is represented as one of a group comprising Mr. Coke, Sir Joseph Banks, Sir John Sinclair, and Mr. Arthur Young.

Professor Warington, than whom no one is more fitted to express an opinion, has favoured me with the following critical estimate of the value of Davy’s work:—

“The lectures profess to be exhaustive and thus present all that Davy had been able to collect on the subject of the relations of chemistry to agriculture during a period of at least 10 years. He appears to have made a careful study of the problems of agriculture for many years, and to be acquainted with English practice, and English experiments. There is but little reference to foreign practice, or foreign opinion, save where the work done has been purely chemical, as e.g. that of Gay Lussac, or Vauquelin. He approaches his subject in a thoroughly scientific manner, taking an independent view of each question, bringing all the knowledge at his disposal to bear upon it, and not hesitating to come to conclusions different from those usually received. The great step taken in these lectures is the assertion that Agriculture must look to Natural Science, and especially to Chemistry, for the explanation of its problems and the improvement of its practice. Davy seems to have been the first, at least in this country, who boldly claimed for ‘Agricultural Chemistry’ the position of a distinct branch of science. He was probably the earliest example of a first-class chemist, who seriously and continuously devoted his best attention to the subject of agriculture.

“The lectures, looked at from a modern standpoint, are of unequal value. The method of food-analysis is very poor, and it is somewhat surprising that the accurate mode of determining nitrogen employed by Gay Lussac is not made use of in Davy’s analyses. Nevertheless he manages to ascertain that spring sown wheat is richer in gluten than autumn sown, and the wheat of hot countries richer than the wheat of temperate regions, statements which are quite correct.

“Lecture VI. is decidedly poor. Davy believes that plants feed on carbonaceous matter by their roots, and this mistaken theory leads him to assign an undue value to organic substances as manures. It seems curious nowadays to find the whole subject of manures treated with hardly any reference to their contents in nitrogen, phosphoric acid, or potash.

“Lecture IV. is one of his best lectures, full of keen observation and suggestive experiment.

“The references to his own agricultural experiments are very numerous; he seems to have made experiments on every subject of inquiry that came before him. There is however no attempt at an extended and thorough investigation of any subject, and for want of this the truth is sometimes missed. Thus in his trials of various ammonium salts as manures he finds the carbonate to be effective, the chloride to be of little value, and the sulphate of no good at all, whereas the last-named salt is now generally chosen as a manure.

“There are some paragraphs that read like the inspirations of genius, though it is now of course difficult to tell to what extent his statements and opinions were warranted by the facts then known. He gives a wonderfully correct idea of the action of peas or beans in rotation, even including the statement that they obtain their nitrogen from the atmosphere.”

Although his time and energy were necessarily largely absorbed by the demands of the Managers, Davy never lost sight of the subject of voltaic electricity, and at intervals he was able to resume his inquiries upon it. What specially impressed him was the power of the voltaic pile as an analytic agent; and his laboratory journals, preserved at the Royal Institution, record the results of numerous trials on the behaviour of compound substances under its influence. In spite of innumerable distractions and constant interruptions, due mainly to the precarious position of the Institution, Davy gradually succeeded in unravelling the fundamental laws of electro-chemistry, and in thus importing a new order of conceptions, altogether unlooked for and undreamt of, into science. This really constitutes his greatest claim as a philosopher to our admiration and gratitude. The isolation of the metals of the alkalis, and the proof of the compound nature of the alkaline earths, were unquestionably achievements of the highest brilliancy, and as such appeal strongly to the popular imagination. But they were only the necessary and consequential links in a chain of discovery which, had Davy neglected to make them, would have been immediately forged by others. It is significant that almost immediately after the capital discovery of Nicholson and Carlisle, Dr. Henry of Manchester, the well-known friend and collaborator of Dalton, should have made the attempt to separate the presumed metallic principle of potash by the agency of voltaic electricity.

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