With like success did the English turn their attention to the manufacture of silk.  Raw material was imported from Southern Europe and Asia ready spun, and the chief labour lay in the twisting of fine threads.  Until 1824 the heavy import duty, four shillings per pound on raw material, greatly retarded the development of the English silk industry, while only the markets of England and the Colonies were protected for it.  In that year the duty was reduced to one penny, and the number of mills at once largely increased.  In a single year the number of throwing spindles rose from 780,000 to 1,180,000; and, although the commercial crisis of 1825 crippled this branch of industry for the moment, yet in 1827 more was produced than ever, the mechanical skill and experience of the English having secured their twisting machinery the supremacy over the awkward devices of their competitors.  In 1835 the British Empire possessed 263 twisting mills, employing 30,000 workers, located chiefly in Cheshire, in Macclesfield, Congleton, and the surrounding districts, and in Manchester and Somersetshire.  Besides these, there are numerous mills for working up waste, from which a peculiar article known as spun silk is manufactured, with which the English supply even the Paris and Lyons weavers.  The weaving of the silk so twisted and spun is carried on in Paisley and elsewhere in Scotland, and in Spitalfields, London, but also in Manchester and elsewhere.  Nor is the gigantic advance achieved in English manufacture since 1760 restricted to the production of clothing materials.  The impulse, once given, was communicated to all branches of industrial activity, and a multitude of inventions wholly unrelated to those here cited, received double importance from the fact that they were made in the midst of the universal movement.  But as soon as the immeasurable importance of mechanical power was practically demonstrated, every energy was concentrated in the effort to exploit this power in all directions, and to exploit it in the interest of individual inventors and manufacturers; and the demand for machinery, fuel, and materials called a mass of workers and a number of trades into redoubled activity.  The steam-engine first gave importance to the broad coal-fields of England; the production of machinery began now for the first time, and with it arose a new interest in the iron mines which supplied raw material for it.  The increased consumption of wool stimulated English sheep breeding, and the growing importation of wool, flax, and silk called forth an extension of the British ocean carrying trade.  Greatest of all was the growth of production of iron.  The rich iron deposits of the English hills had hitherto been little developed; iron had always been smelted by means of charcoal, which became gradually more expensive as agriculture improved and forests were cut away.  The beginning of the use of coke in iron smelting had been made in the last century, and