has been before drawn to the unauthorized attribution of some of these discoveries to another author, they will hardly be prepared for the following statement of its contents which appears in the pages of Lord Brougham: 'The discoveries of Dr. Black on carbonic acid and latent heat appear to have drawn Mr. Cavendish's attention to the cultivation of pneumatic chemistry; and in 1766 he communicated to the Royal Society his experiments for ascertaining the properties of carbonic acid and hydrogen gas. He carried his mathematical habits to the laboratory; and not satisfied with showing the other qualities which make it clear that these two aeriform substances are each sui generis, and the same from whatever substances, by whatever processes they are obtained: nor satisfied with the mere fact that one of them is heavier and the other much lighter than atmospheric air,-he inquired into the precise numerical relation of their specific gravities with one another and with common air, and first showed an example of weighing permanently-elastic fluids: unless, indeed, Torricelli may be said before him to have shown the relative weight of a column of air and a column of mercury: or the common pump to have been long ago compared in this respect air with water. It is, however, sufficiently clear that neither of these experiments gave the relative measure of one air with another: nor, indeed, could they be said to compare common air with either mercury or water, although they certainly showed the relative specific gravities of the two bodies, taking air for the middle term or common measure of their weights.' It is not easy to accumulate, within so short a compass, so many errors of fact and reasoning. Mr. Cavendish did not prove that inflammable airs are the same, by whatever processes or from whatever substances they are derived: he did not assume, but was the first to prove, that fixed air was heavier, and the inflammable air, which was aftewards called hydrogen, was much lighter than atmospheric air: he was not the first to weigh or to determine the specific gravity of a permanently elastic fluid; the weight of a given bulk of common air having been determined by Galileo, Otto Guerike, and with considerable accuracy by Hawksbee, to whose determination Mr. Cavendish himself refers in an elaborate Note to the very Memoir under consideration. The relative weights of a column of equal length and capacity of air and of mercury, or of air and of water, are not involved in the Torricellian experiment, or in that of a common pump; nor is there any sense in which the specific gravity of common air can be considered, in connexion with them, as a middle term or common measure of those of mercury and water. We fear that it would not be safe to pursue the examination of this singular passage farther, as it might lead our readers to impute to Lord Brougham an ignorance of some of the most elementary principles of natural philosophy, if they were not fortified against such a conclusion a conclusion by a knowledge of his various critical and other labours, during more than half a century, in almost every branch of literature and science. It is difficult, however, to refer to a single page of the scientific part of Lord Brougham's volume, which does not present some similar example of inaccuracy of statement or of reasoning, the result, as we are inclined to believe, of a rapidity of composition, and a neglect-we had almost said a contempt of original authorities, which is equally fatal to philosophical correctness and historical truth: of this kind is the account which he has given of the object proposed, and the process followed, in Mr. Cavendish's celebrated experiment for determining the density of the earth :— It was,' says he, about ten years after the conclusion of his chemical labours, that he (Mr. Cavendish) engaged in some important experiments upon the force of attraction. It occurred to him that he could measure that force, and thereby ascertain the density of the earth, by accurately observing the action of bodies suddenly exhibited in the neighbourhood of a horizontal lever nicely balanced, loaded with equal leaden balls, of a small size, at its two ends, and protected from all aerial currents by being enclosed in a box. In that box a telescope and a lamp were placed, that the motions of the lever might be carefully observed. On approaching the external leaden balls made use of, whose diameter was eight inches, to the small ones enclosed and near the lever, it was found that a horizontal oscillation took place. This was measured; and the oscillation caused by the earth on a pendulum being known, as well as the relative specific gravities of lead and water, it was found, upon a medium of his observations, that the earth's density is to that of water as eleven to two.'-Lives, &c., p. 442. We had prepared a commentary upon this extraordinary exposition of a well-known experiment, but those of our readers who are familiar with the original memoir (which will form a lasting monument of the mathematical and philosophical powers and practical skill of its illustrious author) will probably think we have exercised a sound discretion in suppressing it. It is difficult to conceive a more ingenious and entire distortion, not merely of nearly every step in the process itself, but likewise of nearly every principle involved in it. But to return to the chemical labours of Mr. Cavendish. Between the publication of this memoir and those on the composition of water and of nitric acid in the years 1784 and 1788, he continued to prosecute his chemical researches with a success proportionate to his great skill and accuracy in devising and executing experiments and his cautious habits of reasoning upon the legiti mate conclusions to which they lead. Amongst his published papers is one on the Rathbone-place waters, which gave the first example of the accurate analysis of mineral waters, and which was also also important as showing the conditions under which the salts of lime and magnesia (their bicarbonates) are held in solution by them: another is upon the eudiometer of Fontana, an instrument which Priestley originally invented, but which received great improvements in his hands, and enabled him to determine the proportion of oxygen in the atmosphere and in its mixture with other gases with extreme accuracy, and thus to disprove the plausible inferences which the less cautious observations of Dr. Priestley and Dr. Ingenhouz had given rise to, that the oxygen in the air we breathe exists in variable proportions in different localities, and was a proximate cause of their healthiness or unhealthiness. His perfect command of this instrument (for it required to be skilfully and cautiously used) contributed in no slight degree to the successful prosecution of many of his most important subsequent researches. But Mr. Cavendish's published Papers during this period are of much less importance than those which existed in MSS. only, before the appearance of the Appendix to Mr. Harcourt's address, where abstracts of several of them are printed, and some of them entire. In the year 1765, when Dr. Black's discoveries on latent heat scarcely extended beyond the students of his class at Glasgow, we find him, says Mr. Harcourt, with no other information respecting them than the report of a single fact,* deducing all the laws of the generation and destruction of heat from an independent and elaborate series of experiments which the world has never heard of, including the determination of the specific heats of a variety of substances, such as wax, spermaceti, and mercury, with various other metals and metallic alloys. The heat generated by condensing the vapour of steam is shown to be 952°, a very remarkable approximation to the result (so important in the theory of the steam-engine) which was subsequently established by the laborious researches of Watt. The heat produced by thawing snow was shown to be 150°, the result given by Black being 140°. These remarkable experiments preceded by sixteen years the first published notice of Dr. Black's discoveries on this subject, which was given by Wilcke in the Stockholm Transactions for 1781. Another MS. containing Experiments on Arsenic,' written in 1765, and in a form prepared for publication, showed that he had anticipated Scheele by sixteen years in the discovery of the acid of arsenic, its relation to the oxide and regulus, and in the complete examination of its salts; and it further appears from a Paper upon which was written Communicated to Dr. Priestley,' that he first That, in distilling waters or other liquors, the water in the worm-tub is heated thereby much more than it would be by mixing with it a quantity of boiling water equal to that which passes through the worm.' distinguished distinguished nitrogen from the other kinds of unrespirable and incombustible gases, and proved by experiment that atmospheric air consists of two parts, one of which in the combustion of charcoal is converted into fixed air, whilst the other is a mephitic gas sui generis. This discovery, one of the most considerable in the history of chemistry, is authenticated by the reference made to it by Priestley in his paper on Airs' in the Philosophical Transactions for 1772, though the conclusions which it contains are, as was not uncommon with that author, incorrectly stated. He had prepared likewise a fourth part to his paper on Factitious Airs,' containing experiments on the airs produced by distillation from animal and vegetable substances, such as hartshorn shavings, wainscot, and tartar, which were found to yield inflammable air of a kind altogether different, both in specific gravity and explosive power, from the hydrogen or inflammable air which he had examined in his first paper. It could hardly be expected that Lord Brougham, after the specimen which we have ventured to quote of his scientific criticisms on other labours of Mr. Cavendish, should condescend to notice these remarkable researches; and we accordingly find that they are passed over altogether without observation, however important they may be in the estimate which a careful biographer would form of his scientific character. It is quite true that a material distinction should be made between contemporary and posthumous claims to discoveries, unless the latter are supported by the most unquestionable documentary or other authority; and in no case should the rights of prior publication be disputed, unless what was thus made public can be clearly shown to have been in some degree consequent upon a knowledge of the antecedent labours of some other person not so prompt to lay his researches and discoveries before the world. The application of this principle, which is one of primary importance in the history of inventions and discoveries, would assign to Mr. Cavendish the honour of having first ascertained the compound constitution of the atmosphere, and also of one, at least, of its constituents: but it would confer upon him no claim to a participation in the honour which must for ever be awarded to Black and to Watt for their discoveries in latent and specific heat. Before we proceed to the consideration of the next great epoch in the scientific life of Mr. Cavendish, the discovery of the decomposition of water and of the consequences to which it led, let us briefly recall the attention of our readers to some of the accessions which the science of pneumatic chemistry received from other labourers. One of the most remarkable of these was Dr. Priestley, whose researches researches were devoted almost exclusively to the chemistry of the gases. Their results are recorded in six volumes of Experiments and Observations on different kinds of Airs,' which were published between 1775 and 1786, and which appear to have enjoyed an uncommon degree of popularity. They are written in a light and agreeable style, detailing his successes and his failures with equal candour and openness, and laying open his entire chemical mind to the observation of his readers. He was very ingenious in devising experiments, and dexterous in his manipulations; and though the processes which he followed and the means which he had at his command were generally insufficient to secure that minute and rigorous accuracy which is equally necessary for the establishment of great truths and the exclusion of great errors, yet it may be safely asserted that few persons have contributed so great a number of valuable facts to the science of chemistry. He affected no profound philosophical views, and the character of his mind was altogether unequal to them; he generally adopted at once the most obvious conclusions which his experiments appeared to justify, and he modified or abandoned them upon further investigation with almost equal facility. On one point only was his philosophical faith perfectly stable and unalterable: he was an entire believer in the truth of the phlogistic theory, and invariably expressed all his conclusions in its language. No facts, however stubborn and inexplicable, could shake the sincerity of his convictions of its truth, and he continued to maintain and defend it to the end of the century, when it had been abandoned as untenable by every other chemist of eminence in Europe. The most considerable discovery of Dr. Priestley was oxygen gas, which he denominated dephlogisticated air, it being assumed that the two constituents of the atmosphere are distinguished by the separation of phlogiston from one of them and its union with the other, which was therefore denominated phlogisticated air. He investigated many of the most important functions of this air in the vegetable and animal kingdom, and even in the process of combustion, with great ingenuity and success;—and his happy application of its union with nitrous gas to form nitrous acid to the construction of the eudiometer, enabled him and Mr. Cavendish not merely to separate it from other gases with which it might be mixed, but likewise to test its presence and to estimate its quantity -a most important process in analytical chemistry when applied to an element which presents itself so constantly in chemical products. It would be foreign to our present purpose to attempt to enumerate in detail the various discoveries and researches of Dr. Priestley they formed a storehouse of facts which contemporary chemists |