The most important feature of the invention, of course, was the drawing out or attenuating of the cotton by rollers revolving at different speeds. But it was also essential that proper mechanism should be provided by which twist would be put into the yarn to make it sufficiently strong; and furthermore, it was necessary to arrange for the attenuated and twisted cotton to be automatically guided and coiled up or wound up into a convenient form. As we have seen, the drawing out of the cotton finer he accomplished by the Drawing Rollers originally invented by Lewis Paul, while for the latter purpose he successfully adapted the principle already existing in the Saxony wheel, used in the linen manufacture, with which he probably became acquainted during his residence at Preston. It should not be forgotten that Hargreaves had introduced into the commercial world his Jenny, a few years anterior to Arkwright's water frame becoming so successful. These two machines were more or less in rivalry, but not perhaps to that extent which many would suppose. From the very first it was found that the frame of Arkwright's was much more suitable for warp or twist yarns, _i.e._, the longitudinal threads of a cloth, whereas Hargreaves' machine was more adapted for the production of weft yarns, _i.e._, the transverse threads of a cloth. Now it cannot be too strongly remarked that, at the present time, after the lapse of a century, the same state of things practically obtain in the improved machines of to-day; Hargreaves' machine being represented by the system of intermittent spinning upon the improved self-actor mule, while Arkwright's water frame is represented by the system of continuous spinning upon the modern Ring Spinning frame. While weft yarn is now almost entirely produced on the mule, warp yarns are in many cases now obtained from the Ring Frames, this latter system at the present time being greatly on the increase and daily becoming more popular. The Carding Engine was greatly improved by Arkwright's many useful improvements, especially that of the Doffer comb, being entirely his own. The effect of this comb is fully described in the chapter dealing with manipulation of the cotton by the Carding Engine. Paul was probably the first, in 1748, to invent the Carding Machine. His inventions seemed to hang fire until introduced into Lancashire, when they were adopted by a Mr. Peel, Arkwright and others. The chief defects, perhaps, of this machine was the absence of proper means for putting the cotton on the revolving cylinder and having it stripped when sufficiently carded. Hence the great value of Arkwright's stripping comb.