Watt's engine, once fairly started, was not long in making its way into general use. The first steam-engine used in Manchester was erected in 1790; and now it is estimated that in that district, within a radius of ten miles, there are in constant work more than fifty thousand boilers, giving a total power of upwards of one million horses. And the united steam power of Great Britain is considered equal to the manual labour of upwards of four hundred millions of men, or more than double the number of males on the face of the earth. From the factory at Soho, Watt's improved engines were dispersed all over the country, especially in Cornwall--the firm receiving the value of a third part of the coal saved by the use of the new machine. In one mine, where there were three pumps at work, the proprietors thought it worth while, it is said, to purchase the rights of the inventors, at the price of L2500 yearly for each engine. The saving, therefore, on the three engines, in fuel alone, must have been at least L7500 a year. In the first year of the present century, Watt withdrew himself entirely from business; but though he lived in retirement, he did not let his busy mind get rusty or sluggish for want of exercise. At one time he took it into his head that his faculties were declining, and though upwards of seventy years of age, he resolved to test his mental powers by taking up some new subject of study. It was no easy matter to find one quite new to him, so wide and comprehensive had been his range of study; but at length the Anglo-Saxon tongue occurred to him, and he immediately applied himself to master it, the facility with which he did so, dispelling all doubt as to the failing of his stupendous intellect. He thus busied himself in various useful and entertaining pursuits, till close upon his death, which took place in 1819. Extraordinary as was Watt's inventive genius, his wide range of knowledge, theoretic and practical, was equally so. Great as is the "idea" with which his name is chiefly associated, he was not a man of one idea, but of a thousand. There was hardly a subject which came under his notice which he did not master; and, as was said of him, "it seemed as if every subject casually started by him had been that he had been occupied in studying." He had no doubt a rapid faculty of acquiring knowledge; but he owed the versatility and copiousness of his attainments above all to his unwearied industry. He was always at work on something or other, and he may truly be called one of those who-- "Could Time's hour-glass fall, Would, as for seed of stars, stoop for the sand, And by incessant labour gather all."