The imports of raw cotton slowly increased to 2,000,000 in 1720, and to 3,000,000 lbs. in 1751. In 1764, the year in which Hargreaves introduced the spinning jenny, they were still not higher than 4,000,000 lbs. But the successive inventions, during the course of about three decades, alike of Hargreaves, Arkwright, Crompton, Cartwright and others gave such an impetus to the industry that by 1800 the importation of raw cotton (greatly facilitated by the further invention, in 1793, of Eli Whitney's appliance for separating cotton from the cotton seed) had risen to 52,000,000 lbs., while the value of all kinds of cotton products exported increased between 1765 and 1800 from £800,000 to £5,800,000. This rapid progress would not, however, have been possible but for the facilities for obtaining cheap power afforded by the condensing steam-engine of James Watt, who had taken out a patent for his invention in 1769, though it was not till 1776 that he built and sold his first engine, on which he further improved in 1781. Steam-power, of far greater force {188}and utility, and capable of being produced anywhere, thus took the place of the water-power, only available alongside streams, on which, as we have seen, the earlier success of the woollen industry, especially as carried on among the hills of Yorkshire, had been established. It was by water-power that the spinning machine so recently introduced by Sir Richard Arkwright was operated until James Watt had shown that steam could be used to better advantage. Then the setting up at Papplewick, Nottinghamshire, in 1785, of a steam-engine for the operation of cotton machinery marked, also, the decline of domestic manufactures and the advent of that factory system which was to bring about a complete transformation in the industrial conditions of the United Kingdom. Yet just as the improvements in cotton production would have been incomplete without the steam-engine, so, also, would the invention even of the steam-engine have been of little service but for an abundant supply of coal, and but, also, for the possession of a ready and economical means of moving the coal from the localities where it was to be found to those where it was wanted for the purposes of the "steam age" that was about to open. The greater demand for fuel and the increased facilities for supplying it led to the greater development of various inland coal-fields, in addition to those already long in operation in the Newcastle district, and having there the advantages of river and sea as an aid to distribution. The need, also, of coal for the operation of the steam-engine in the countless number of new industries or new works that followed on James Watt's improvements had an important influence on fixing the location of fresh industrial centres.