CHAPTER XX. HISTORY OF THE DISCOVERY OF THE COMPOSITION OF WATER MR. STATE OF THAT SCIENCE PREVIOUS TO 1783 BLACK AND PRIESTLEY IN 1783,-one of the busiest of those ten years of his life which may thus be said to have teemed with experiments and inventions,-Mr. Watt had the further honourable distinction of making and publishing his famous discovery of the Composition of Water. It must be added, though we do so with regret, that, as in his greatest mechanical inventions, so in this matter also, he experienced the unpleasant necessity of vindicating his own just claims from the unexpected, and, as we believe, most men will be of opinion, the unjustifiable, interference of others. It was an occasion, however, on which the firmness, moderation, and true greatness of his mind were signally manifested; and the circumstances of which, as displayed in his Correspondence on the subject, have contributed in every way to increase his good name. His principal inventions connected with the steam-engine, with all their prodigious results, were founded, as we have seen, on the attentive observation of great philosophical truths; and the economy of fuel, increase of productive power, and saving of animal labour, which gradually ensued, all originated in the sagacious and careful thought with which he investigated the nature and properties of heat. The department of physical science with which, next to mechanics, he may be said to have been at one time most familiar, and which long continued in some measure to occupy his leisure hours, was Chemistry. With what success he studied it, we know from the testimony of the most eminent among his contemporaries who directed their attention especially to that subject, and many of whom were his frequent correspondents. "He was equally distinguished," said the late illustrious President of the Royal Society, Sir Humphry Davy, "as a natural philosopher and a chemist, and his "inventions demonstrate his profound knowledge of those sci"ences."* The numerous experiments which he made with a view to the attainment of the great principles of which he was in search, are further commended by the same accomplished and able judge, as difficult, delicate, and refined. 66 It is stated in the Memoirs of his friend and neighbour, the celebrated botanist Dr. Withering, that "in his estimation, "Mr. Watt's abilities and acquirements placed him next, if "not superior, to Newton ;" + a judgment dictated, no doubt, by the kind partiality of a friend, but showing the estimation in which Mr. Watt's talents were held by an able and discerning man of science. How intently he watched the phenomena, how deeply he penetrated into the causes of chemical action, might be conceived from his friend Robison's description of him as "a philosopher in the most exalted sense of "the word, who never could be satisfied with a conjectural knowledge of any subject, and who grudged no labour nor study to acquire certainty in his researches." The highest merit certainly attaches to his chemical discoveries, and deep interest must be felt by all who attend to the history of their origin and progress, from the fact that he was in this, as in almost every other part of learning, self-taught. He has himself, on one of the very few occasions on which he ever made public any of his writings through the medium of the press, (almost all the others being only communications to the Royal Society, which were ordered to be printed,) taken pains to correct the statements of Professor Robison on this point. That gentleman, in dedicating to him his edition of Dr. Black's Lectures, called him Dr. Black's pupil, declared that he had attended two courses of his lectures, and even alluded * Speech in 1824.-Translation of Arago's 'Eloge,' p. 191. + Tracts and Memoir of Dr. Wi thering, by his Son, 1822. Vol. i. p. 46. Preface to Black's Lectures. to his professing to owe his improvements on the steamengine to the instructions he had received from that eminent teacher. This, however, is altogether erroneous; and Mr. Watt has lamented that the necessary avocations of his business at that time prevented his attending either Dr. Black's or any other lectures. But he repeatedly acknowledged the information and pleasure he derived from the conversation of that enlightened philosopher, as well as from the friendship of such men as Robert Simson and Dr. Dick, both distinguished cultivators of kindred branches of natural knowledge. In establishing himself at Soho, he retained his habits of intimate correspondence with Dr. Black, who had then, for more than twenty years, made known his discovery of carbonic acid gas, and for at least sixteen had annually explained his theory of latent heat in his lectures, in which, also, for the first time, he developed the doctrine of the capacities of bodies for heat, (or that of specific heat); and who, after spending ten years of academical labour in the University of Glasgow, had, in 1766, accepted that professorial chair in Edinburgh, which for thirty years longer he continued to render famous.t We have much pleasure in being able, on indisputable authority, to attribute the public announcement of Dr. Black's theory of latent heat to a period considerably earlier than had formerly been named, even by Dr. Black's zealous admirer and pupil, Lord Brougham. His Lordship says that Dr. Black meditated on that theory, investigated it by experiment, and taught it in his lectures, at least as early as 1763. But the following extract from his letter to Mr. Watt, of 15th March, 1780, furnishes information more precise, and assigns with certainty a much earlier date to so admirable a discovery. "I began," says the Doctor, "to give the doctrine "of latent heat in my lectures at Glasgow, in the winter 1757-58, which I believe was the first winter of my lecturing "there, or, if I did not give it that winter, I certainly gave "it in the 1758-59, and I have delivered it every year "since that time in my winter lectures, which I continued to give at Glasgow until winter 1766-67, when I began to lec"ture in Edinburgh." 66 In the same letter he mentions by name many distinguished foreigners, as well as natives of this country, who had attended some of the earliest courses of his lectures, and had then heard his explanations of that remarkable theory; adding, that about 1760-61, or soon after, he read a paper on the subject, in the Philosophical or University Club at Glasgow, and thus concluding:-"I could bring a multitude of "other evidences to prove the early date of my doctrines on "this subject." We need hardly observe, that none who are duly aware of the modesty and carelessness of fame, the scrupulous veracity, and exact observation of facts, which distinguished that truly learned and excellent person, can imagine any other kind of evidence more convincing than his own testimony. After the publication of so decisive a record, further exposure of the attempts which have sometimes been made to rob Dr. Black of his great and well-earned glory is wholly superfluous. Priestley, who, in the year 1774, had effected by far the most remarkable and brilliant of his numerous discoveries, (that, viz. of oxygen gas), came in 1780 to Birmingham; where he afterwards usually resided, till driven away from that place in 1791, by the violence of a riotous mob, under the influence of religious and political exasperation. During the whole of his stay in that neighbourhood, which has been well described as at that period "a region of rare talents," he was on terms of habitual and friendly intercourse with Mr. Watt, frequently conversing with him on those scientific subjects which were of the greatest interest to them both; and we find him publicly and repeatedly acknowledging the pleasure he derived from such congenial society.* It is impossible to conceive a more complete contrast than was presented by the mode of philosophising adopted by Black and Priestley respectively. The one, calm and reflective, conducted his experiments often with such simple apparatus as came readiest to his hand, but always with studied neatness, accuracy, and success; carefully watching every step of the well-considered process, and deducing, with all the force of exact demonstration, either the overthrow of some long-settled belief, or the description of a new substance, or the establishment on solid foundations of a theory altogether unsuspected by any other inquirer; his conclusions being as much distinguished for their originality, beauty, and usefulness, as any thing to be found in the whole history of inductive research. The other, with warm zeal and untiring perseverance, but with little idea of order, and an imperfect acquaintance with the true first principles of science, contrived experiments of infinite number and variety, observed them with lively interest, and often with a just perception; and minutely recorded the smallest particulars, which in their progress he noticed, if not always for his own advantage, yet certainly for the great benefit of others. But to the higher objects of philosophical inquiry and generalisation, he was little accustomed to apply the many great and luminous truths which he was the first to make known; and in more than one instance he even plunged deep into error, which some of his contemporaries, neither better informed on other points, nor gifted with superior powers of observation, were able to avoid. It is curious to find his well-known candour thus expressing his own views of the manner in which scientific research ought to be conducted, at a period nearly twenty years after he had received the Copley medal for his inquiries into several kinds of air, and had, almost at the same time, completed his grand and undisputed discovery of oxygen gas: **Philosophical Transactions,' 1783, p. 416. |