observed afterwards on their sides. In fact, water was present which was not present before.

The mixture was in this case fired by passing an electric spark through the vessel; and it is now known that the effect produced was the combination of the hydrogen, which formed part of the mixture of airs in the vessel with the oxygen, which also formed part of the same mixture.

It appears, from expressions in Warltire's letter, that the same experiment had been previously made by Priestley, and the same result observed by him.

The inference deduced from this by Warltire, and apparently acquiesced in by Priestley, was, that whenever hydrogen was fired in atmospheric air, the moisture, which is always more or less sustained in the latter, was deposited; but neither of these chemists perceived the real cause of the production of the water.

In the beginning of 1783, and not later than the 21st of April, this experiment of Warltire and Priestley was repeated by Cavendish, with this difference, that, instead of exploding the mixture of hydrogen and common air, Cavendish exploded a mixture of hydrogen and oxygen. He observed that water was present after the explosion, but inferred nothing.

In a published paper dated April, 1783, Priestley announced a further and most important result of his experiments. This was, that in examining the weight of water produced by the explosion of a mixture of oxygen and hydrogen, that weight was found to be precisely equal to the sum of the weights of the two gases, which disappeared in the process.

Immediately on observing this, Priestley, being then, as has been already stated, Watt's near neighbour, communicated to the latter what he had observed; upon which Watt immediately, viz. by a letter dated the 26th of the same month, declared that the inevitable consequence which followed from Priestley's observations was, that water was a substance compounded of oxygen and hydrogen deprived of

a quantity of heat which was previously latent in them.* The letter containing this inference was communicated immediately by Priestley to Sir Joseph Banks, then President of the Royal Society, to be laid before that body; and it is accordingly printed with its proper date in the 74th volume of the Philosophical Transactions.

About two months after the date of Mr. Watt's letter just quoted, Lavoisier made experiments on the combustion of oxygen and hydrogen, and read a memoir before the Academy of Sciences in Paris, in which his views of the formation of water by the combination of these gases were developed. This paper, by Lavoisier, was afterwards printed in the Memoirs of the Academy in the year 1784. The experiments are there stated to have been made in the month of June, 1783; and it is stated that Sir Charles Blagden, who was present at the experiments, told Lavoisier that Mr. Cavendish had already burned the same gases in close vessels, and obtained a very sensible quantity of water.

On the 15th of January, 1784, the celebrated paper by Cavendish, entitled "Experiments on Air," was read before the Royal Society, and in this paper the composition of water by the union of oxygen and hydrogen is explained.

In a controversy which afterwards ensued on the respective

*The following are the words in which Watt makes this remarkable announcement to Priestley :

"Let us now consider what obviously happens in the deflagration of "the inflammable (hydrogen) and dephlogisticated air (oxygen). These "two kinds of air unite with violence; they become red hot, and upon cooling, totally disappear. When the vessel is cooled, a quantity of "water is found in it equal to the weight of the air employed. This "water is then the only remaining product of the process; and water, light, and heat are all the products.

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"Are we not then authorised to conclude, that water is composed of dephlogisticated air (oxygen) and phlogiston (hydrogen), deprived of part of their latent or elementary heat; that dephlogisticated or pure air (oxygen) is composed of water deprived of its phlogiston (hydrogen), "and united to elementary heat and light; and that the latter are con"tained in it in a latent state, so as not to be sensible to the thermometer or to the eye; and if light be only a modification of heat, or a circumstance attending it, or a component part of the inflammable air (hy"drogen), then pure or dephlogisticated air (oxygen) is composed of "water deprived of its phlogiston (hydrogen), and united to elementary "heat."

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claims of Cavendish and Lavoisier to credit for the discovery of the composition of water, Sir Charles Blagden stated that he had told Lavoisier, in June, 1783, more than Lavoisier acknowledged, that he had not only told him that water was produced by the combustion of the gases, but that his information embraced the whole theory of the composition of water. This declaration of Blagden was subsequent in date to January, 1784, and there is no evidence of any explanation of this theory, verbal or otherwise, having been given by Cavendish, or any other person, antecedent to April, 1783.

From this brief statement of the facts and dates it will appear that the merit of the discovery of the FACT, that the weight of water resulting from the combustion of oxygen and hydrogen, is equal to the sum of the weights of the oxygen and hydrogen which disappear in the combustion, is due to Priestley; and that the merit of the INFERENCE from that fact, that water is a compound body, whose constituents are oxygen and hydrogen, is due to Watt.* Whether those who subsequently deduced the same inference, and promulgated the same theory, were or were not informed of Mr. Watt's solution of the phenomenon, or what credit may be due to any person, however eminent, who at any time posterior to Mr. Watt's letter to Priestley, asserted that they had, at a time antecedently to that, made the same inference without having published it, or communicated it in such a manner as to establish their claim upon rational and credible evidence, are questions which we shall not here discuss, being contented with establishing the right of Mr. Watt to the merit of the discovery of the THEORY which explained the FACT discovered by Priestley.

Even in his declining years, after he had withdrawn from the active pursuits of his business, the least exeitement was sufficient to call into play the slumbering powers of his inventive genius. No object could present itself to his notice

Those who desire to investigate this controversy more in detail will find very full information on the subject in the Translation of Arago's Eloge, with notes and appendix by J. P. Muirhead, Esq. Murray, London, 1839.

without receiving from that genius adaptation in form and construction to useful purposes. As an example of this restless activity of mind the following anecdote may be mentioned: :

A company at Glasgow had erected on the right bank of the Clyde extensive buildings and powerful engines for supplying water to the town. After this expense it was found that a source of water, of very superior quality, existed on the left bank of the river. To change the site of the establishment, after the expense which had been incurred in its erection could not be contemplated, and they therefore proposed to carry across the bottom of the river a flexible suction pipe, the mouth of which should terminate in the source from which the pure water was to be derived. This pipe was to be supported by a flooring constructed upon the bed of the river; but it was soon apparent that the construction of such a flooring on a shifting and muddy bottom, full of inequalities, and under several feet depth of water would require a greater expenditure of capital than could with propriety be afforded. In this difficulty the aged mechanician, for whom Glasgow itself had been the earliest stage of professional labour, was applied to, and instantly solved the problem. His attention is said to have been attracted by a lobster which had been served at table: he set himself about to contrive how, by mechanism, he could make an apparatus of iron with joints which should have all the flexibility of the tail of the lobster. He therefore proposed that an articulated suction-pipe, capable of accommodating itself to all the inequalities and to the possible changes of the bed of the river, should be carried across it; that this flexible pipe should be two feet in diameter, and one thousand feet in length. This project the company accordingly caused to be executed after the plans and drawings of Watt with the most complete suc

* An account of this remarkable apparatus, accompanied by an engraving made from a drawing supplied by Watt, was communicated by Sir John Robison to the Edinburgh Philosophical Journal in 1820. See vol. iii. p. 60.

Among the less prominent, though not less useful services rendered by Watt to his country, may be mentioned the introduction of the use of chlorine in bleaching. That invention of Berthollet was introduced into England by Watt after his visit to Paris at the close of the year 1786. He constructed all the necessary apparatus for it, directed its erection, and superintended its first performances. He then left it to his wife's father, Mr. Macgregor, to carry on the processes.

When the properties of the gases began to occupy the attention of chemists, attempts were made to apply them as a means of curing diseases of the lungs. Dr. Beddoes pursued this inquiry with great activity, and established, through the means of private subscription, at Clifton, an institution in which this method of cure was carefully investigated. The Pneumatic Institution (for so it was called) has been rendered celebrated for having at its head Humphry Davy, just then commencing his scientific career. Among its founders was also numbered James Watt. Not content, however, with affording the institution the sanction of his name, he designed and caused to be constructed, at Soho, the apparatus used for making the gases and administering them to the patients.

As the exalted powers of the mind of Watt, unfolded in his numerous mechanical and philosophical inventions and discoveries, have commanded the admiration and respect of his species, the affection and love of his fellow men would not have been less conciliated, had the qualities of his heart, as developed in his private and personal relations, been as well known as the products of his genius.

In the year 1764, Watt being then in the twenty-ninth year of his age, married his cousin, Miss Miller. At this time he had fallen into a state of despondency from his disappointments, which produced a serious attack of nervous illness. The accomplishments and superior understanding, the mildness of temper and goodness of disposition of his wife, soon restored him to health. Of this marriage four children, two sons and two daughters, were the issue. Two of these children died in infancy; another, a daughter, was married to Mr. Miller of Glasgow; and the fourth is the