a later period Watt also invented the indicator, by means of which the actual horse power of an engine could be ascertained. This beautiful series of inventions in a measure may be said to have perfected the machine, and at the present time the condensing steam engine differs in no material respect from the engine as Watt left it. While residing at Birmingham, Mr. Watt's house became the resort of many learned men. In the meetings of the Lunar Society, held at Soho House, originated his experiments on water, and between him and Cavendish is the honour divided of having first promulgated the theory of its composition. During the dispute which arose upon this subject, Watt's reply, on a friend regretting that another should have carried off this honour, is worth recording, as showing the modest dignity of his character: "It matters not," said he, "whether Cavendish discovered this or I, it is discovered." In the year 1800 Mr. Watt, having acquired an ample competency, ceased to take an active part in the business of the firm, and the remainder of his life was spent in retirement; but his active mind, still unwearied, continued to follow its natural bent. On two occasions afterwards, in 1811 and 1812, he gave proofs of the undiminished powers of his inventive genius. In the one instance he was induced, by his grateful recollections of his residence in Glasgow, to assist the proprietors of the waterworks there with a plan for supplying the town with better water, by means of a suction pipe laid across the Clyde to reach to the other side, where water of a very superior quality might be procured. This pipe was formed of cast iron, with flexible joints, after the manner of a lobster's tail, so as to accommodate itself to the bed of the river, and fully answered the purpose for which it was designed. In the other instance he was prevailed upon, by the earnest solicitation of the Lords Commissioners of the Admiralty, to attend a deputation of the Navy Board, and to give, with his friend Captain Huddart and Mr. J. Jessop, an opinion upon the works then carrying on at Sheerness Dockyard, and the further ones projected by Messrs. Rennie and Whitby. On this occasion he no less gratified the gentlemen associated with him by the clearness of his general views, than by his knowledge of the details; and he received the thanks of the Admiralty for his services. In 1814 he yielded to the wishes of his friends, of Dr. Brewster especially, and undertook a revision of Professor Robison's articles on steam and steam-engines for an early edition of the _Encyclopædia Britannica_, which he enriched with valuable notes, containing his own experiments on steam, and a short history of his principal improvements upon the engine itself. Among other mechanical contrivances of Mr. Watt's may be mentioned: a machine for copying letters; an instrument for measuring the specific gravity of fluids; a regulator lamp; a plan for heating buildings by steam; and a