‘that water is composed of dephlogisticated and inflammable air.’ Dr. Priestley received this letter in London, submitted it to Sir Joseph Banks, president of the Royal Society, and to Dr. Blagden, the intimate friend of Cavendish, and his secretary. This letter was to have been read before the Royal Society, but Watt requested that the public reading of it might be delayed until he should examine some new experiments, said by Dr. Priestley to contradict his theory.
Cavendish's memoir having been read 15 Jan. 1784, Watt's first letter was, according to his own request, read at the Royal Society on 22 April, his second letter being read on 29 April. In these communications Watt writes, referring to Dr. Priestley: ‘If my deductions have any merit, it is to be attributed principally to the perspicuity, attention, and industry with which you have pursued the experiments which gave birth to them, and to the candour with which you receive the communications of your friends.’ From this it is evident that Watt himself admits his obligations to Dr. Priestley, and we have seen that Cavendish and Priestley were friendly correspondents; consequently it may safely be concluded that the speculations on the composition of water were the common subjects of talk in the scientific societies of London and Birmingham.
J. A. De Luc [q. v.], the Genevese philosopher, was a fellow of the Royal Society at this time, and it was from him that Watt first heard of Cavendish's paper. Weld, the assistant secretary, in his ‘History of the Royal Society,’ says that ‘in July of the same year his paper was printed in the “Transactions,” bearing the erroneous date of 1784 instead of 1783, which stands upon the manuscript.’ Many were deceived, and among them Cuvier, by this error. As soon as it was discovered, Cavendish wrote to the editor of one of the principal foreign journals to correct it. The discussion which prevailed for some time in France and England as to the priority of Cavendish or Watt as discoverers was unpleasantly aggravated by the errors of the dates printed, and yet more so by two interpolations, made after the reading of Cavendish's paper, by Dr. Blagden, who was appointed secretary to the Royal Society on 5 May 1784, and to whom was entrusted the superintendence of the printing of both Watt's letters, and who made the interpolations in Cavendish's contribution.
The only conclusion to which we can arrive is, that both Cavendish and Watt made about the same time experiments on air and water; that they framed hypotheses which were of an analogous character, differing mainly in respect to elementary heat, which Watt regarded as a material entity, but which Cavendish rejected as insufficient to account for the observed phenomena. They both worked honestly, in ignorance of each other's studies, and they both arrived at similar conclusions.
If Cavendish had been more communicative, there is no doubt he would have avoided the annoyance of the claims made by Watt and other investigators to a discovery the merit of which was justly his own. It is satisfactory to record that in 1785 Watt became a fellow of the Royal Society; he then formed the acquaintance of Cavendish, and they terminated their scientific rivalries in the most amicable manner.
It is necessary to mention a ‘Mémoire où l'on prouve par la décomposition de l'eau, que ce fluide n'est point une substance simple,’ &c., by MM. Meusnier et Lavoisier, printed in 1784; a second paper on the same subject by Lavoisier alone; and a ‘Mémoire sur le résultat de l'inflammation du gaz inflammable et de l'air déphlogistiqué dans des vaisseaux clos,’ par M. Monge, printed in 1786. There is, however, satisfactory evidence to prove that the French chemists had been previously informed of the discoveries of Cavendish and Watt.
The use of light in promoting the growth of plants was most carefully investigated by Cavendish, but the conclusions which he drew from his experiments were vitiated by the theory of phlogiston, which had not yet been entirely abandoned.
The views entertained by Cavendish on specific and latent heat greatly advanced our views, and, associated with the fine investigations made by Dr. Black, paved the way to the more philosophical deductions of the present day.
After 1785, Cavendish made no new discoveries. His papers on heat, the original records of which prove that this investigation was commenced in 1764, were written out for the use of a friend, but he published no part of them until nineteen years after most of the experiments had been completed, and then a trifling portion only appears incidentally in a paper on the ‘Freezing of Mercury,’ read at the Royal Society in 1783.
It has been suggested that the reason why those researches on heat were never published was that Cavendish had considerable reluctance to enter into even the appearance of rivalry with Dr. Black.
In 1772 and in 1776 Cavendish was engaged in investigating the principal phenomena of electricity, and two papers on the
