Though the invention of the working steam-engine—the king of machines—belongs, comparatively speaking, to our own epoch, the idea of it was born many centuries ago. Like other contrivances and discoveries, it was effected step by step—one man transmitting the result of his labours, at the time apparently useless, to his successors, who took it up and carried it forward another stage,—the prosecution of the inquiry extending over many generations. Thus the idea promulgated by Hero of Alexandria was never altogether lost; but, like the grain of wheat hid in the hand of the Egyptian mummy, it sprouted and again grew vigorously when brought into the full light of modern science. The steam-engine was nothing, however, until it emerged from the state of theory, and was taken in hand by practical mechanics; and what a noble story of patient, laborious investigation, of difficulties encountered and overcome by heroic industry, does not that marvellous machine tell of! It is indeed, in itself, a monument of the power of self-help in man. Grouped around it we find Savary, the military engineer; Newcomen, the Dartmouth blacksmith; Cawley, the glazier; Potter, the engine-boy; Smeaton, the civil engineer; and, towering above all, the laborious, patient, never-tiring James Watt, the mathematical-instrument maker. Watt was one of the most industrious of men; and the story of his life proves, what all experience confirms, that it is not the man of the greatest natural vigour and capacity who achieves the highest results, but he who employs his powers with the greatest industry and the most carefully disciplined skill—the skill that comes by labour, application, and experience. Many men in his time knew far more than Watt, but none laboured so assiduously as he did to turn all that he did know to useful practical purposes. He was, above all things, most persevering in the pursuit of facts. He cultivated carefully that habit of active attention on which all the higher working qualities of the mind mainly depend. Indeed, Mr. Edgeworth entertained the opinion, that the difference of intellect in men depends more upon the early cultivation of this _habit of attention_, than upon any great disparity between the powers of one individual and another.