As an example of the beneficial effects produced upon the efficiency of an individual engine by the first application of this system of inspection, the case of the Stray Park engine may be mentioned. This engine,.constructed by Boulton and Watt, had a sixty inch cylinder, and when first reported in 1811, its duty amounted to 16,000,000 pounds. After having been reported on for three years, its duty was found to have increased to 32,000,000; this estimate being taken from the average result of twelve months' performance. Its duty was doubled in less than three years.

It will appear, by inspection of the duties registered in the preceding table, that the augmentation of the efficiency of the engines has not been the effect of any great or sudden improvement, but has rather resulted from the combination of a great number of small improvements in the details of the operation of these machines. In these improvements more is due to the successful application of practical experience than to any new principles developed by scientific research. Mr. John Taylor, in his "Records of Mining," has traced the successive improvements on which the increased duty of engines depends, and has connected these improvements with their causes in the order of their dates. The following results, abridged from his estimates, may not be uninteresting:

In 1769, soon after the date of the earliest discoveries of Mr. Watt, but before they had come into practical application, Smeaton computed that the average duty of fifteen atmospheric engines, working at Newcastle-on-Tyne, was 5,590,000. The duty of the best of these engines was 7,440,000, and that of the worst 3,220,000.

In 1772, Smeaton commenced his improvements on the atmospheric engine, and raised the duty to 9,450,000.

In 1776, Watt obtained a duty of 21,600,000.

At this time Smeaton acknowledged that Watt's engines gave a duty amounting to double that of his own.

In 1778-79, Watt reported a duty of 23,400,000. From 1779 to 1788, Watt introduced the application of expansion, and raised the duty to 26,600,000.

In 1798, an engine by Boulton and Watt, erected at Herland, was reported as giving a duty of 27,000,000.

This engine, which was probably the best which at that time had ever been erected, attracted the particular attention of Mr. Watt, who, on visiting Cornwall, went to see it, and had many experiments tried with it. It was under the care of Mr. Murdock, the agent of Messrs. Boulton and Watt in Cornwall. When Mr. Watt inspected it he pronounced it perfect, and that further improvement could not be expected. How singular an instance this of the impossibility, even of the most sagacious, to foresee the results of mechanical improvement! In twenty years afterwards the average duty of the best engine was nearly 40,000,000, and in forty years it was above 84,000,000.

NOTICE OF THE LIFE OF MR. WATT. HIS FRIENDS AND ASSOCIATES AT BIRMINGHAM.INVENTION OF THE COPYING PRESS. HEATING BY STEAM. - DRYING LINEN BY STEAM. THEORY OF THE COMPOSITION OF WATER. FIRST MARRIAGE OF WATT.-DEATH OF HIS FIRST WIFE.-HIS SECOND MARRIAGE. DEATH OF HIS YOUNGER SON.EXTRACTS FROM HIS LETTERS. CHARACTER OF WATT BY LORD BROUGHAM. BY SIR WALTER SCOTT BY LORD JEFFREY.OCCUPATION OF HIS OLD AGE. INVENTION OF MACHINE FOR COPYING SCULPTURE. HIS LAST DAYS. - MONUMENTS.

(179.) HAVING brought this historical analysis of the invention and application of the steam engine to the date of the decease of the illustrious man, to the powers of whose mind the world stands indebted for the benefits conferred upon

mankind by that machine, it will perhaps not be deemed an improper digression in this work, to devote some pages to a notice of the principal labours of the same mind in other departments of art and science, and to circumstances connected with his personal history and the close of his life, which cannot fail to possess general interest.

At the period when Watt, having connected himself in partnership with Boulton, went to reside at Soho, near Birmingham, a number of persons, some of whom have since attained great celebrity by their discoveries and their works, and all of whom were devoted to inquiries connected with the arts and sciences, resided in that neighbourhood. Among these may be mentioned PRIESTLEY, whose discoveries in physical science have rendered his name immortal; DARWIN, the philosopher and poet; WITHERING, a distinguished physician and botanist; KEIR, a chemist, who published a translation of Macquer, with annotations; GALTON, the ornithologist; and EDGEWORTH, whose investigations respecting wheeled carriages and other subjects, have rendered him well known. A society was formed by these and other individuals, of which Boulton and Watt were leading members, the meetings of which were held monthly on the evening of full moon, and which was thence called the Lunar Society. At the meetings of this society, subjects connected with the arts and sciences were discussed, and out of those discussions occasionally arose suggestions not unattended with important and advantageous consequences. At one of these meetings, Darwin stated that he had discovered a pen formed with two quills, by means of which, at a single operation, an original and a copy of a letter might be produced. Watt almost instantly observed that he thought he could find a better expedient, and that he would turn it in his mind that night. By the next morning the COPYING PRESS was invented, for which he afterwards obtained a pa

tent.

This machine, which is now so generally used in countinghouses, consists of a rolling-press, by which a leaf of thin paper, previously damped, is pressed upon the letter to be copied. The writing, of which the ink is not yet quite dry, leaves its impression upon the thin paper thus pressed upon

it, and the copy taken in this manner is read through the semi-transparent paper. If a letter be written with ink suitable for this purpose, a copy may be taken at any time within several hours after the letter is written.

The method of heating apartments and buildings by steam, which has since been improved and brought into extensive use, was likewise brought forward by Watt. Although this contrivance had been previously pointed out by Sir Hugh Platt about the middle of the seventeenth century, and by Colonel Cooke in 1745, yet these suggestions remained barren. Mr. Watt gave detailed methods of heating buildings by steam*; and also invented a machine for drying linen by steam, a description of which he communicated to Dr. Brewster, which was read in December, 1824, before the Society for promoting Useful Arts in Scotland.+

But the circumstance, exclusive of those connected with the invention of the steam engine, which is by far the most memorable in the career of Watt, is the share which he had in the discovery of the composition of water. As this circumstance has recently excited much interest, and led to some controversy, we shall here state, as distinctly as possible, the leading facts connected with it.

Water, which was so long held to be a simple element, has, in modern times, been proved to be a substance consisting of two aeriform bodies or gases chemically combined. These two gases are those called in chemistry oxygen and hydrogen. If eight grains weight of oxygen be mixed with one grain weight of hydrogen, and the mixture be submitted to such effects as would cause the chemical combination of these two airs, it would be converted into nine grains weight of pure water.

If, on the other hand, nine grains weight of pure water be submitted to any conditions which would separate its constituent parts, the result would be eight grains weight of oxygen gas, and one grain weight of hydrogen gas. There are a variety of methods in physics by which these effects would be

* See Buchanan on the Economy of Fuel and Management of Heat, especially as it relates to heating and drying by means of Steam.

+ See Brewster's Edinburgh Encyclopædia, article STEAM-DRYING MACHINE.