But there were more conspicuous improvements effected in the mule during the first six or seven years after it was made public, and among them were those of Henry Stones of Horwich, who, it is believed, was the first maker of mules after Crompton, either for his own use or for the use of others. His improvements consisted in the introduction of metal rollers, in place of wooden ones, and of a self-acting contrivance to stop them when they had given out the required length of roving, while various devices came into use for measuring the number of revolutions necessary for this purpose. One effect of the improvements of Stones was to allow the mule to be enlarged to 100 or 130 spindles.[382] Soon afterwards a man named Baker of Bury introduced other improvements which enabled the whole machine to be further enlarged, and another man, Hargreaves of Toddington (Tottington near Bury?), contrived a method for bringing out the carriage.[383] [Footnote 382: _Ibid._, pp. 332-333.] [Footnote 383: _Ibid._, 333-334.] But, in addition to improvements, there was also a development in connection with the mule in these early years. This was the invention of a machine called the “Billy” by a man at Stockport who, it may be noticed, again received a premium as a reward for his ingenuity.[384] Up to this time the mule had been used solely for the spinning of yarn. The rovings for spinning had to be made either on the spinning-wheel, or by Arkwright’s machinery. The “Billy” was a modification of the mule, or rather a combination of the mule and the jenny; but, instead of spinning rovings into yarn, it made the carded cotton into rovings. With this machine rovings could be made for the use of the mule, the jenny, or even the water-frame, to any required degree of fineness, and at a greatly reduced cost.[385] This modification of the mule, therefore, extended its own use, but it was not so with the jenny, although it was the jenny-spinners who subscribed the premium for the inventor. [Footnote 384: _Ibid._, p. 331.] [Footnote 385: Kennedy, _ibid._, pp. 331-332.]