To the close of his life, Watt continued to take great pleasure in inventing. It had been the pursuit of his life, and in old age it became his hobby. "Without a hobby-horse," said he, "what is life?" He proceeded to verify his old experiments, and to live over again the history of his inventions. When Mr. Kennedy of Manchester asked him, at one of his last visits to Heathfield, if he had been able, since his retirement from business, to discover anything new in the steam-engine, he replied, "No; I am devoting the remainder of my life to perfect its details, and to ascertain whether in any respect I have been wrong."
But he did not merely confine himself to verifying his old inventions. He also contrived new ones. One of the machines that occupied his leisure hours for many years was his machine for copying statuary. We find him busy with it in 1810, and he was still working upon it in the year of his death, nearly ten years later. The principle of the machine was to make a cutting tool or drill travel over the work to be executed, in like ratio with the motion of a guide-point placed upon the bust to be copied. It worked, as it were, with two hands; the one feeling the pattern, the other cutting the material into the required form. The object could be copied either of the full size, or reduced with the most perfect accuracy to any less size that might be required. In preparing the necessary tools, Watt had the able assistance of his friend Murdock, who was always ready with his kindly suggestions and criticisms. In January, 1813, Watt wrote to him,—"I have done a little figure of a boy lying down and holding out one arm, very successfully; and another boy, about six inches high, naked, and holding out both his hands, his legs also being separate. But I have been principally employed in making drawings for a complete machine, all in iron, which has been a very serious job, as invention goes on very slowly with me now. When you come home, I shall thank you for your criticisms and assistance."
The material in which Watt executed his copies of statuary were various,—marble, jet, alabaster, ivory, plaster of Paris, and mahogany. Some of the specimens we have seen at Heathfield are of exquisite accuracy and finish, and show that he must have brought his copying-machine to a remarkable degree of perfection before he died. There are numerous copies of medallions of his friends,—of Dr. Black, De Luc, and Dr. Priestley; but the finest of all is a reduced bust of himself, being an exact copy of Chantrey's original plaster-cast. The head and neck are beautifully finished, but there the work has stopped, for the upper part of the chest is still in the rough. Another exquisite work, than which Watt never executed a finer, is a medallion of Locke in ivory, marked "January, 1812." There are numerous other busts, statuettes, medallions,—some finished, others half-executed, and apparently thrown aside, as if the workman had been dissatisfied with his work, and waited, perhaps, until he had introduced some new improvement in his machine.
Watt took out no patent for the invention, which he pursued, as he said, merely as "a mental and bodily exercise." Neither did he publish it, but went on working at it for several years before his intentions to construct such a machine had become known. When he had made considerable progress with it, he learned, to his surprise, that a Mr. Hawkins, an ingenious person in the neighbourhood, had been long occupied in the same pursuit. The proposal was then made to him that the two inventors should combine their talents and secure the invention by taking out a joint patent. But Watt had already been too much worried by patents to venture on taking out another at his advanced age. He preferred prosecuting the invention at his leisure merely as an amusement; and the project of taking out a patent for it was accordingly abandoned. It may not be generally known that this ingenious invention of Watt has since been revived, and applied, with sundry modifications, by our cousins across the Atlantic, in fashioning wood and iron in various forms; and powerful copying-machines are now in regular use in the Government works at Enfield, where they are employed in rapidly, accurately, and cheaply manufacturing gun-stocks!
