From the beginning, the effect of this invention was to multiply many times the amount of yarn that could be spun by a spinner, and the size of the jenny was soon increased. In 1767 it was said to contain eight spindles; when Hargreaves took out his patent in 1770 the specification mentioned sixteen or more; in 1784 the number had increased to eighty; and ultimately as many as one hundred and twenty are said to have been introduced.[263] Although the jenny did not make the rovings, and its movements depended upon hand power, it represented a great advance in spinning, and its mechanism was so simple that it could be worked by children.[264] The thread it produced, however, was not completely satisfactory for the warp in cotton goods, as it was not “capable of giving that hardness of twist and fineness which was necessary to form the threads of the warp.”[265] [Footnote 263: Espinasse, _ibid._, pp. 322, 327.] [Footnote 264: Ogden, _ibid._, p. 87.] [Footnote 265: Guest, _British Cotton Manufacture_ (1828), p. 147. Ogden states that the larger jennies were used for making warps until they were superseded by the water-frame (_ibid._, p. 91).] This defect was supplied by the invention of spinning by rollers patented by Arkwright--the water-frame as it came to be called--as the characteristic feature of the yarn thus spun was its suitability for the warp. The jenny and the water-frame, therefore, were complementary rather than substitutional machines. When the patent for spinning by rollers was taken out in 1769, as with the jenny, it was still intended that the rovings should be made on the spinning-wheel. But with Arkwright’s method, instead of the rovings being attenuated by a long stretch, the operation was performed by their passing between rollers moving at different velocities, which had the same effect. For the twisting and the winding of the thread the “Flier” spindle mentioned in connection with the “Saxony” wheel was utilised. Consequently, the spinning and winding operations proceeded simultaneously, whereas with the jenny they were intermittent.[266] [Footnote 266: _Souvenir of Royal Visit to Bolton_, pp. 16-17.] Before Arkwright obtained his second patent in 1775, sometimes called the “carding” patent, the roller method had been extended to the rovings, and as he and others had effected the improvements, already mentioned, in the carding machine, the whole of the operations required in transforming the raw cotton into yarn could be performed by machinery.[267] [Footnote 267: Espinasse, _ibid._, p. 400.]