Wind was too inconstant and uncontrollable, and besides, in England,
 the birthplace of modern industry, the use of water power preponderated
 even during the manufacturing period. In the 17th century attempts had already been made to turn two pairs of millstones with a single water-wheel.
 But the increased size of the gearing was too much for the water power,
 which had now become insufficient, and this was one of the circumstances
 that led to a more accurate investigation of the laws of friction. In the
 same way the irregularity caused by the motive power in mills that were
 put in motion by pushing and pulling a lever, led to the theory, and the
 application, of the fly-wheel, which afterwards plays so important a part
 in modern industry. [12] In this way, during the manufacturing period, were developed the first scientific and technical elements of Modern
 Mechanical Industry. Arkwright’s throstle spinning mill was from the very
 first turned by water. But for all that, the use of water, as the predominant
 motive power, was beset with difficulties. It could not be increased at
 will, it failed at certain seasons of the year, and, above all, it was
 essentially local. [13] Not till the invention of Watt’s second and so-called double-acting steam-engine, was a prime357 mover
 found, that begot its own force by the consumption of coal and water, whose
 power was entirely under man’s control, that was mobile and a means of
 locomotion, that was urban and not, like the waterwheel, rural, that permitted
 production to be concentrated in towns instead of, like the water-wheels,
 being scattered up and down the country, [14] that was of universal technical application, and, relatively speaking, little affected
 in its choice of residence by local circumstances. The greatness of Watt’s
 genius showed itself in the specification of the patent that he took out
 in April, 1784. In that specification his steam-engine is described, not
 as an invention for a specific purpose, but as an agent universally applicable
 in Mechanical Industry. In it he points out applications, many of which,
 as for instance, the steam-hammer, were not introduced till half a century
 later. Nevertheless he doubted the use of steam-engines in navigation.
 His successors, Boulton and Watt, sent to the exhibition of 1851 steam-engines
 of colossal size for ocean steamers.