tains a greater or less quantity of atmospheric air, and it was impossible to introduce one into the condenser without the other. Being brought with the water into contact with the hot steam, it would expand, and entering the cylinder prevent the formation of a vacuum, for being a permanent gas it could not be condensed like the vapour, steam. In consequence of the usefulness of the pump in preventing the accumulation of air, it is generally known by engineers under the name of the air pump, although this is only a part of the important office it performs.

No sooner had Watt proved the value of these inventions than another was suggested to his mind, which dispensed with atmospheric pressure, and converted his contrivance into a steam engine, every motion being produced by that vapour. In the construction of Newcomen's engine, it had been customary to cover the piston with water in order to make it steam-tight. Watt perceived how disadvantageous this would be to his contrivance, for not only would the passage of any portion of the fluid into the lower part of the cylinder cause an immediate formation of steam, but air also would be introduced, interfering in a still greater degree with the production of a vacuum and the working of the engine, to say nothing of the effect of the water in cooling the cylinder in its passage up and down with the piston. The consideration of this subject led him to inquire as to the possibility of entirely surrounding the cylinder with steam,

so that the downward stroke might be produced by the expansive force of that fluid instead of the pressure of the atmosphere. This design he carried into practice, and surrounded the cylinder with a casing, now called a jacket, filling the interval between them with steam from the boiler. The top of the casing fitted closely, and an aperture was accurately bored in the centre, through which the piston rod moved steam and air-tight. The downward stroke

being now made by steam, the force was always under control, being increased or diminished at pleasure; the exterior as well as the interior of the cylinder was kept at a sufficient temperature, and every provision was made against the intrusion of atmospheric air into working spaces.

We need not point out the evidences of deep thought, penetration, discrimination, and industry displayed by Watt in the pursuit of the object he had resolved to attain, and in describing his inventions we have sufficiently exhibited their importance. Wanting the capital necessary for the introduction of his improvements, he fixed his models in a place called Delft House, in Glasgow, and invited the attention of those whom he thought best able to judge their merit or appreciate their importance. All admired, but none offered assistance. Nor was this strange. Little was it to be expected that an obscure mechanic, not thirty years of age, whose whole life seemed to have been spent either in scientific reveries or in the con

struction of philosophical toys, was destined to produce a machine which should give an impetus to industry, advance the conditions of society, open a communication between nations the most distant, demand from legislators a revision of laws, and from all men, kings and people, submission, praise, and gratitude. Nor did the indifference with which his discoveries were received greatly affect him; he was willing to wait, if that were necessary, but he could no longer continue his former employment.

Having closed his workshop at Glasgow, Mr. Watt devoted himself to the duties of a civil engineer. For three years, he was actively engaged in this pursuit, and was intrusted with several large and important enterprises. Among other works, he made a plan for a canal to convey coal from the Monkland collieries to Glasgow, which he executed. He also prepared a survey for a navigable canal through the isthinus of Crinan, a work afterwards executed by the elder Rennie. He also made investigations of, and reported improvements for, the harbours of Ayr, Glasgow, and Greenock. To these labours may be added the deepening of the river Clyde, the rendering navigable the rivers Forth and Devon, and the water of Leven; the planning of a canal from Macrihanish Bay to Campbeltown, and of another between the Grand Canal and the Harbour of Borrowstounness; the building of Hamilton and Rutherglen bridges, and the surveys and plans for the Caledonian Canal.

During this long period his engine was in abeyance, and he waited hoping for the time when he might secure its adoption. In the year 1768, he was employed as a civil engineer by Dr. Roebuck, the proprietor of the Carron Iron Works. To him he mentioned the improvements he had made in the atmospheric engine. A patent and partnership was suggested by Roebuck, and Watt consented to make over to his employer a two-third share of the profits to be derived from the invention, in consideration of the advantages he was likely to receive from his large capital and extensive connexion. A patent was accordingly taken out, and an experimental engine was made, which more than fulfilled the anticipations of the inventor. Difficulties as they arose were one after another met, and everything seemed to promise an unexampled success, when Dr. Roebuck found himself involved in pecuniary difficulties in consequence of the failure of his undertaking in the Borrowstounness coal and iron works, and was unable to supply the necessary funds for the prosecution of the design.

CHAPTER V.

PROCEEDINGS AT THE SOHO WORKS.

HOWEVER disappointed Mr. Watt may have been by the failure of his hopes through the inability of Dr. Roebuck to carry on the projected manufacture of his engines, he was not long left without the assistance he required. His inventions had already become known to many intelligent men engaged in manufactures, and among others to Mr. Matthew Bolton, of Soho Works, near Birmingham. This gentleman was at that time carrying on one of the largest and most successful metal trades in England, and was alike distinguished for his business habits and commercial enterprise. In the moment of Watt's perplexity, Bolton made an offer for the purchase of Dr. Roebuck's share in the patents; terms were made, and the agreement was completed. In the early part of the year 1774, Mr. Watt removed to Soho, where a portion of the manufactory was placed under his entire control, for the erection of a foundery and all other shops and machinery necessary for carrying out his inventions upon the largest scale and in the most perfect manner.