tion of horse-power drifted, resulting in as many as five different kinds, see the ‘Proceedings of the Royal Agricultural Society’ (2nd ser. vol. ix. Cardiff meeting, No. 17, p. 55).
In 1785 Watt took out his last patent, No. 1485. This was for constructing furnaces, &c., the object being to attain better combustion and the avoidance of smoke. The invention appears to have been based on correct principles, and to have been employed with success to some little extent; but it was dependent very largely on the attention of the stoker, and was of but little practical use.
It has been thought well not to interrupt the sequence of the engine patents, and thus a patent as early as 1780 (No. 1244) has been passed over in order of its date, as it related to a matter entirely unconnected with the steam engine; it was, however, of great utility, and is now universally employed. This was the invention of copying letters by means of a specially prepared ink, which would give an impression on a damped sheet of a suitable paper when the writing and the damped paper were pressed together. Probably but few of the thousands upon thousands who, throughout all civilised nations, have their letter-copying books and presses are aware that this most useful process is due to the great James Watt.
When the success of the Watt engine was fully established, attempts were made to invent engines which should have the same advantages, but which should not be within the ambit of Watt's patent. One of these attempts was by Edward Bull, in the case of pumping engines for mines. The sole alteration he made was to invert the cylinder over the shaft of the mine and to connect the pumps directly to the piston-rod, thus doing away with the main beam; but he retained the separate condenser with its air-pump. Another attempt was made by Jonathan Carter Hornblower [see under Hornblower, Jonathan]. He proposed to employ the expansive principle by allowing the steam to pass from one working cylinder to a second working cylinder of increased capacity—a construction which prevails to-day under the title of the compound engine, and that, in the further development of three cylinders in series, is practically universally employed in all large steam vessels, whether used for war or for commerce. Hornblower, however, could not dispense with the separate condenser and air-pump, and his engines were thus infringements of Watt's original patent. From 1792 to 1800 Watt and his partner were engaged in vindicating his patent, and in putting a stop to these infringements. Actions were brought in the common pleas against Bull and against Hornblower, with whom was joined as defendant one Maberley. In each case the infringement was all but admitted, the defenders' arguments being addressed to the invalidity of the patent. In each case the jury found a verdict for the plaintiff. In each case the full court of common pleas by a majority determined the patent to be bad, on (speaking as a layman) grounds of the vagueness of the specification, due to the advice of the amateurs in patent matters to whom allusion has already been made, and in each case there was appeal. On appeal the patent was upheld, and the long litigation came to an end, after years of anxiety suffered by Watt and his partner, and after very heavy expenditure, as may be gathered from the fact that in the four years between 1796 and 1800 the costs were 6,000l. Watt used to speak of his patent as ‘his well-tried friend.’
By the kindness of Mr. George Tangye of Soho and of Heathfield Hall (at one time Watt's residence), the writer has had access to much of the correspondence between Boulton and Watt and their sons during the period these actions were going on; it is most interesting, and it shows also the charming character of the relations subsisting between these four men. In April 1781 Boulton, after complaining to Watt of a difference he had with a partner in his separate business, continued: ‘However, as to you and I [sic], I am sure it is impossible we can disagree in the settling of our accounts, as there is no sum total in any of them that I value so much as I do your esteem, and the promotion of your health and happiness; therefore I will not raise a single objection to anything that you shall think just, as I have a most implicit confidence in your honour.’
Watt's love of science was not confined to physics. He had from the time of his early life in Glasgow been devoted to chemistry, and, when settled in Birmingham, the pursuit of chemical science was stimulated by his intimate connection with such men as Priestley, Keir, Small, and Wedgwood. These, with others, constituted the ‘Lunar’ Society, who met monthly at about the time of the full moon. It was no doubt his steady pursuit of chemical science, even in the midst of all his steam-engine labours, that led Watt to the brilliant discovery of the composition of water. That Watt did make this independent discovery is undoubted. Whether it was made prior to a similar discovery by Henry Cavendish
