THE EDINBURGH NEW PHILOSOPHICAL JOURNAL. An Estimate of the Philosophical Character of Dr Priestley. By WILLIAM HENRY, M. D., F. R. S. &c. &c.* THE HE principal source of the materials of the following sketch, is the work in which the discoveries of Dr Priestley were originally announced to the public. It consists of six volumes in octavo, which were published by him at intervals between the years 1774 and 1786; the first three under the title of " Experiments and Observations on different kinds of Air;" and the last three under that of "Experiments and Observations relating to various Branches of Natural Philosophy, with a continuation of the Observations on Air." These volumes were afterwards methodized by himself, and compressed into three octavos, which were printed in 1790. As a record of facts, and as a book of reference, the systematized work is to be preferred ; but as affording materials for the history of that department of science which Dr Priestley cultivated with such extraordinary success, and, still more, for estimating the value of his discoveries, and adjusting his station as an experimental philosopher, the simple narrative, which he originally gave in the order of time, supplies the amplest and the firmest ground-work. In every thing that respects the history of this branch of experimental philosophy, the writings and researches of Dr Priestley, to which I have alluded, are peculiarly instructive. They * Read to the first meeting of the British Association for the Promotion of Science, at York, September 28. 1831. A beautiful Biographical Memoir of Dr Priestley, by Baron Cuvier, is printed in the Number for July 1827 of this Journal. VOL. XIII. NO. XXV.-JULY 1832. A are distinguished by great merits, and by great defects; ter of which are wholly undisguised by their author. veils, with perfect frankness, the whole process of rea which led to his discoveries; he pretends to no more than belonged to him, and sometimes disclaims even which he was fairly entitled; he freely acknowledges h takes, and candidly confesses when his success was the re accident, rather than of judicious anticipation; and by historically and analytically, he exhibits the progressive in ment of his views, from their first dawnings to their final a tinct development. Now, with whatever delight we ma template a systematic arrangement, the materials of which been judiciously selected, and from which every thing ha excluded that is not essential to the harmony of the gener sign, yet there can be no question that, as elucidating the tions of the human mind, and enabling us to trace and ap ate its powers of invention and discovery, the analytic m of writing has decided advantages. To estimate, justly, the extent of Dr Priestley's claim to sophical reputation, it is necessary to take into account the of our knowledge of gaseous chemistry at the time he his inquiries. Without underrating what had been already by Van Helmont, Ray, Hooke, Mayow, Boyle, Hales, Mach Black, Cavendish, and some others, Priestley may be safel firmed to have entered upon a field, which, though not al ther untilled, had yet been very imperfectly prepared to the rich harvest, which he afterwards gathered from it. very implements with which he was to work were for the part to be invented; and of the merits of those which he di vent, it is a sufficient proof that they continue in use to this with no very important modifications. All his contrivances collecting, transferring, and preserving different kinds of air, for submitting those airs to the action of solid and liquid. stances, were exceedingly simple, beautiful, and effectual. T were chiefly, too, the work of his own hands, or were constr ed under his directions by unskilled persons; for the class of genious artists, from whom the chemical philosopher now der such valuable aid, had not then been called into existence ets; the lat r. He un E reasoning, pre sagacity ven that to -es his mis- the opera- m to philont the state e he began ready done Macbride, e safely afnot altoge d to yield The n it. r the most he did into this day, ivances for of air, and Liquid subual. They - constructclass of innow derives istence by owledge of the Philosophical Character of Dr Priestley. 3 the general principles of chemistry, and almost without practice in its most common manipulations;-restricted by a narrow income, and at first with little pecuniary assistance from others ;compelled, too, to devote a large portion of his time to other pressing occupations, he nevertheless surmounted all obstacles; and in the career of discovery outstripped many who had long been exclusively devoted to science, and were richly provided with all appliances and means for its advancement. It is well known that the accident of living near a public brewery at Leeds, first directed the attention of Dr Priestley to pneumatic chemistry, by casually presenting to his observation the appearances attending the extinction of lighted chips of wood in the gas which floats over fermenting liquors. He remarked, that the smoke formed distinct clouds floating on the surface of the atmosphere of the vessel, and that this mixture of air and smoke, when thrown over the sides of the vat, fell to the ground; from whence he deduced the greater weight of this sort of air than of atmospheric air. He next found that water imbibes the new air, and again abandons it when boiled or frozen. These more obvious properties of fixed air having been ascertained, he extended his inquiries to its other qualities and relations; and was afterwards led by analogy to the discovery of various other gases, and to the investigation of their characteristic properties. It would be inconsistent with the scope of this essay to give a full catalogue of Dr Priestley's discoveries, or to enumerate more of them than are necessary to a just estimate of his philosophical habits and character. He was the unquestionable author of our first knowledge of oxygen gas, of nitrous oxide, of muriatic, sulphurous, and fluor acid gases, of ammoniacal gas, and of its condensation into a solid form by the acid gases. Hydrogen gas was known before his time; but he greatly extended our acquaintance with its properties. Nitrous gas, barely discovered by Dr Hales, was first investigated by Priestley, and applied by him to eudiometry. To the chemical history of the acids derived from nitre, he contributed a vast accession of original and most valuable facts. He seems to have been quite aware that those acids are essentially gaseous substances, and that they might be exhibited as such, provided a fluid could A 2 Dr Henry's Estimate ofondy be found that is incapable of absorbing or acting upon He obtained, and distinctly described†, the curious cr compound of sulphuric acid with the vapour of nitrous more correctly, of sulphuric and hyponitrous acids, whic of rare occurrence, was forgotten, and has since been vered, like many other neglected anticipations of the sa thor. He greatly enlarged our knowledge of the importa of metals, and traced out many of their most interesting to oxygen and to acids. He unfolded, and illustrated ple and beautiful experiments, distinct views of combust the respiration of animals, both of the inferior and higher of the changes produced in organized bodies by putre and of the causes that accelerate or retard that process; importance of azote as the characteristic ingredient of substances, obtainable by the action of dilute nitric acid o cle and tendon; of the functions and economy of living bles; and of the relations and subserviency which exist b the animal kingdoms. After trying, without effect, a of methods, by which he expected to purify air vitiated breathing of animals, he discovered that its purity was re by the growth of living and healthy vegetables, freely exp the solar light. It is impossible to account for these and a variety of discoveries, of less importance singly, but forming altoge tribute to science, greatly exceeding, in richness and exten of any contemporary, without pronouncing that their a must have been furnished by nature with intellectual p far surpassing the common average of human endowment we examine with which of its various faculties the mind a Priestley was most eminently gifted, it will, I believe, be that it was most remarkable for clearness and quickness o prehension, and for rapidity and extent of association. On qualities were founded that apparently intuitive percepti analogies, and that happy facility of tracing and pursuing through all their consequences, which led to several of his brilliant discoveries. Of these analogies many were just legitimate, and have stood the test of examination by the cl pon them*. s crystalline ous acid, or, which, being een redisco he same au portant class ing relations ated by simmbustion; of her classes; Outrefaction, cess; of the nt of animal acid on musving vegetaxist between et, a variety ated by the was restored y exposed to ety of other altogether a extent, that heir author tual powers wments. If mind of Dr ve, be found kness of ap1. On these erception of rsuing them of his most ere just and the clearer condition of the Philosophical Character of Dr Priestley. 5 science. But, in other cases, his analogies were fanciful and unfounded, and led him far astray from the path which might have conducted him directly to truth. It is curious, however, as he himself observes, that in missing one thing, of which he was in search, he often found another of greater value. In such cases, his vigilance seldom failed to put him in full possession of the treasure upon which he had stumbled. Finding by experience, how much chance had to do with the success of his investigations, he resolved to multiply experiments, with the view of increasing the numerical probabilities of discovery. We find him confessing, on one occasion, that he "was led on, by a random expectation of some change or other taking place.” In other instances, he was influenced by theoretical views of so flimsy a texture, that they were dispersed by the first appeal to experiment." These mistakes," he observes," it was in my power to have concealed; but I was determined to show how little mystery there is in the business of experimental philosophy; and with how little sagacity, discoveries, which some persons are pleased to consider great and wonderful, have been made." Candid acknowledgments of this kind were, however, turned against him by persons envious of his growing fame; and it was asserted that all his discoveries, when not the fruits of plagiarism, were "lucky guesses," or owing to mere chance*. Such detractors, however, could not have been aware of the great amount of credit that is due to the philosopher, who at once perceives the value of a casual observation, or of an unexpected result; who discriminates what facts are trivial, and what are important; and selects the latter, to guide him through difficult and perplexed mazes of investigation. In the words of D'Alembert, "Ces hazards ne sont que pour ceux qui jouent bien.” The talents and qualifications which are here represented as having characterized the mind of Dr Priestley, though not of the rarest kind, or of the highest dignity, were yet such as admirably adapted him for improving chemical science at the time when he lived. What was then wanted, was a wider field of * These charges, especially that of plagiarism, which had been unjustly advanced by some friends of Dr Higgins, were triumphantly repelled by Dr Priestley, in a pamphlet entitled, "Philosophical Empiricism," published in 1775. |