To English trade the canal opened up the richest of all markets, the market of England itself. Every part of the country was practically thrown open to the manufacturer: and the impulse which was given by this facility of carriage was at once felt in a vast developement of production. But such a developement would have been impossible had not the discovery of this new mode of distribution been accompanied by the discovery of a new productive force. In the coal which lay beneath her soil England possessed a store of force which had hitherto remained almost useless. But its effects were now to make themselves felt. The first instance of the power of coal was shown in utilizing the stores of iron which had lain side by side with it in the northern counties, but which had lain there unworked through the scarcity of wood, which was looked upon as the only fuel by which it could be smelted. In the middle of the eighteenth century a process for smelting iron with coal turned out to be effective; and the whole aspect of the iron-trade was at once revolutionized. In fifty years the annual production of iron in Great Britain rose from under twenty thousand to more than one hundred and seventy thousand tons. During the fifty years that followed it rose to six millions of tons. Iron was to become the working material of the modern world; and it is its production of iron which more than all else has placed England at the head of industrial Europe. But iron was not the only metal which coal drew from the soil to swell the national wealth. The increase in its production was rivalled by that of lead, copper, and tin; and the "mining districts" soon gathered a population which raised them into social as well as economical importance.
But it was not in its direct application to metallurgy that coal was destined to produce its most amazing effects. What was needed to turn England into a manufacturing country was some means of transforming the force stored up in coal into a labour force; and it was this transformation which was now brought about through the agency of steam. Engines in which steam was used as a means of draining mines had long been in use; but the power relied on was mainly that of the weight of the air pressing on a piston beneath which a vacuum had been created by the condensation of steam; and the economical use of such engines was checked by the waste of fuel which resulted from the cooling of the cylinder at each condensation, and from the expenditure of heat in again raising it to its old temperature before a fresh stroke of the piston was possible. Both these obstacles were removed by the ingenuity of James Watt. Watt was a working engineer at Glasgow, whose mind had for some time been bent on the improvement of the steam-engine; but it was not till the spring of 1765, amidst the political turmoil which characterized the early reign of George the Third, that as he strolled on a Sunday afternoon across the Green of Glasgow the means of effecting it burst on him. "I had gone," he says, "to take a walk on a fine Sabbath afternoon. I had entered the Green by the gate at the foot of Charlotte Street, and had passed the old washing-house. I was thinking upon the engine at the time, and had got as far as the herd's house, when the idea came into my mind that as steam was an elastic body it would rush into a vacuum, and if a communication were made between the cylinder and an exhausted vessel it would rush into it, and might there be condensed without cooling the cylinder. I had not walked farther than the Golf-House when the whole thing was arranged in my mind." The employment of a separate condenser, with the entire discarding of any other force in its action save that of steam itself, changed the whole conditions of the steam-engine. On the eve of the American war, in 1776, its use passed beyond the mere draining of mines; and it was rapidly adopted as a motive-force for all kinds of manufacturing industry.