that University as the most precious of relics), perceived the various defects of that machine, and ascertained by experiment their

causes. Watt set to work scientifically from the first. He studied the laws of the pressure of elastic fluids, and of the evaporating action of heat, so far as they were known in his time; he ascertained as accurately as he could, with the means of experimenting at his disposal, the expenditure of fuel in evaporating a given quantity of water, and the relations between the temperature, pressure, and volume of the steam. Then reasoning from the data which he had thus obtained, he framed a body of principles expressing the conditions of the efficient and economic working of the steam engine, which are embodied in an invention described by himself in the following words, in the specification of his patent of 1769:

"My method of lessening the consumption of steam, and consequently fuel, in fire engines, consists of the following principles :"First, That vessel in which the powers of steam are to be employed to work the engine, which is called the cylinder in common fire engines, and which I call the steam vessel, must, during the whole time the engine is at work, be kept as hot as the steam that enters it; first, by inclosing it in a case of wood, or any other materials that transmit heat slowly; secondly, by surrounding it with steam or other heated bodies; and thirdly, by suffering neither water nor any other substance colder than the steam, to enter or touch it during that time.

"Secondly, In engines that are to be worked wholly or partially by condensation of steam, the steam is to be condensed in vessels distinct from the steam vessels or cylinders, although occasionally communicating with them; these vessels I call condensers; and, whilst the engines are working, these condensers ought at least to be kept as cold as the air in the neighbourhood of the engines, by application of water, or other cold bodies.

"Thirdly, Whatever air or other elastic vapour is not condensed by the cold of the condenser, and may impede the working of the engine, is to be drawn out of the steam vessels or condensers by means of pumps, wrought by the engines themselves, or otherwise.

"Fourthly, I intend, in many cases, to employ the expansive force of steam to press on the pistons, or whatever may be used instead of them, in the same manner in which the pressure of the atmosphere is now employed in common fire engines. In cases where cold water cannot be had in plenty, the engines may be wrought by this force of steam only, by discharging the steam into the air after it has done its office.

"Lastly, Instead of using water to render the pistons and other parts of the engines air and steam tight, I employ oils, wax, resinous bodies, fat of animals, quicksilver, and other metals in their fluid state."

The expense of carrying out of Watt's invention was at first defrayed by Dr. John Roebuck, the original projector of the Carron Iron Works. On his retirement from the enterprise, his place was taken by Matthew Boulton of Birmingham, whose liberality and energy furnished all that was necessary to render the genius of Watt practically available. Few patents have had their validity more obstinately contested than that of Watt's great invention; and the successful result of the trials of which it was the subject has greatly contributed to ascertain and fix the interpretation of the patent laws. In 1769, Watt had invented the cutting-off the admission of steam, so as to make it work expansively, as appears from a letter of his to his friend Dr. Small. He began to use that invention in 1776, but did not publish it till 1782, when he patented along with it his invention of the double acting engine. It is certain that before 1778, Watt had invented the double acting steam engine, and the application of the crank to the steam engine; but the latter invention having been pirated and patented by another, Watt invented and patented other methods of producing rotatory from reciprocating motion, which were used until the patent for the crank expired; after which time the use of the crank became general. The adaptation of the steam engine to the production of rotatory motion was the crowning improvement, which led to its employment as the prime mover of every kind of mechanism. În 1784, Watt patented and published his inventions of the parallel motion, the counter for recording the strokes of engines, the throttle valve, the governor for regulating the speed, and the indicator for ascertaining the power, and also a locomotive engine; which last, however, he did not put in practice. The improvements on the steam engine since the time of Watt have chiefly related either to the boiler and furnace, to the details of the mechanism, to the more full development of Watt's principle of using the expansive force of the steam to drive the piston, or to the means of applying the steam engine to the propulsion of carriages and ships. The double cylinder engine was invented by Hornblower in 1781, and was afterwards combined with Watt's condenser by Woolf.

The history of the application of the steam engine to the propulsion of ships has been brought into a very complete state by the compilation, under the direction of Mr. Woodcroft, of abridgments of patents for marine propulsion, together with various documents relative to inventions of that class not patented in Britain.

It appears from the correspondence between Papin and Leibnitz, that Papin was present, in 1698, at a trial of a boat propelled by a machine contrived by Savery, in which paddle wheels were driven by a water wheel, which was itself driven by water raised by means

of Savery's steam engine, already mentioned; and also that Papin himself, in 1707, made either a vessel or a model of a vessel (it is not clear which) on a similar plan, with which he was on his way by the Fulda and Weser to England, when it was taken from him and destroyed by boatmen.

In 1736, Jonathan Hulls patented a steam vessel in which paddle wheels were driven by ratchet work, acted upon by chains or ropes attached to the pistons of atmospheric cylinders.

In 1752, Daniel Bernouilli invented a form of screw propeller, which he proposed to drive by a steam engine.

In 1781 and 1783, the Marquis de Jouffroy executed and used upon the Rhone two steam vessels of considerable size-in the first of which paddle wheels were driven by chains, and in the second by rack work. They are said to have realized a considerable speed.

The early attempts at steam navigation made in France by the Marquis de Jouffroy in 1781 and 1783, in America by Rumsey and Fitch about 1783 and 1784, and in Scotland in 1788 and 1789, by Miller of Dalswinton, Taylor, and Symington, appear to have failed chiefly because of the imperfect nature of the means employed for the transmission of motion from the piston to the propeller. In fact, Watt's invention of the rotative engine, which effects that transmission smoothly and without shocks, was an indispensable step towards the success of steam navigation. Symington, instructed by the previous failure of his engine in Miller's boat, availed himself of that invention, when he built for Lord Dundas, in 1801, the "Charlotte Dundas," which was used in 1802 on the Forth and Clyde Canal, with complete success as a tug, but abandoned owing to an apprehension on the part of the directors of injury to the banks. The "Charlotte Dundas" (fig. V.) had one

Fig. V.-The "Charlotte Dundas," 1801-2. paddle wheel near the stern, driven by a direct acting horizontal

engine, with a connecting rod and crank. The arrangement of her mechanism was such as would be considered creditable at the present day; and she has been justly styled by Mr. Woodcroft "the first practical steamboat."

Fulton having made himself well acquainted with what had been previously done in steam navigation, began to experiment with a small paddle steamer in 1803. In 1804, Stevens ran a steamer between New York and Hoboken, with a screw propeller, driven by one of Watt's engines.

The establishment of steam navigation as a remunerative art was first effected in America, by Fulton, in 1807, on the East river; and in Europe, by Bell, in 1812, on the Clyde. Fulton's vessel, the "Clermont," was propelled by paddles, driven by an engine made by Boulton and Watt. Bell's vessel, the "Comet," was propelled by two pairs of paddle-wheels, driven by an engine

Fig. VI. The "Comet," 1811-12.

of peculiar design (fig. VII.) Since that period the advancement of steam navigation has consisted not so much in the development of new principles, as in the improvement of workmanship, arrangement, and economy of fuel, and the progressive increase of the size, power, and speed of steam-ships, and the extent of their voyages-the largest vessel yet built being the "Great Eastern," 680 feet long, 83 feet broad. This vessel has now been broken up. The largest passenger steamers at the present time are the " Campania" and "Lucania," plying between Liverpool and New York. These vessels measure 601 feet in length by 65 feet broad, and about 38 feet deep; tonnage about 13,000 tons. They have twin screws, driven by triple-expansion engines of 30,000 I.H.P. Average speed on voyage is 21 knots. highest speed attained by large steamers is about 21 knots, but boats of the torpedo class exceed 30 knots.

The

The application of the steam engine to locomotion on land was, according to Watt, suggested by Robison, in 1759. In 1784, Watt