Some old Carding Engines which were used at this time are still in existence, though only used for museum purposes. As will have been gathered in a former chapter dealing with the manipulation of the cotton in the mill, between the Carding Engine and the final process of spinning there are other and important stages of preparation, and in these it is seen how in one respect Arkwright's method of drawing out cotton by revolving rollers was immeasurably superior to the travelling carriage of Hargreaves. The strength of a rope is represented by its weakest parts, and the same may be said of yarn. There can be no doubt that one of Arkwright's greatest difficulties was to give an uniform yarn, and though he successfully launched his new machines he felt there was still much to be done in the direction of remedying yarn which was irregular in thickness and strength. In order to do this, he finally adapted his drawing rollers to what is now the modern drawing frame--a machine quite as largely used, and quite as necessary in present-day spinning, as it was a hundred years ago. It was sought to make this machine do two things. (1) Several slivers of cotton from the Card were put up together at the back, and by means of four pairs of drawing rollers, were reduced to the thickness of one sliver (see the description in chapter vi.). It will be sufficient to say here that this method of doubling and drawing equalises the sliver of cotton by the combination of the thick places with the thin. Doubling is now the reason of the uniformity of the yarns that are produced in such large quantities. (2) The Carding Engine did not by any means lay the fibres of cotton sufficiently parallel to each other, and this process of parallelisation was fully accomplished by the front ends of the fibres being drawn forward more rapidly than their back ends by the drawing rollers revolving at different velocities. Mr. Baines says it was common to perform this operation until the finished sliver contained portions from _several thousand_ carding slivers, but we think he would have been nearer the mark if he had said several hundred; although the higher number may be occasionally reached. Yet again, in order to obtain a thread or yarn of sufficient fineness, it was found necessary to perform some of the attenuation of the cotton sliver as it left the drawing frame and before it reached the final spinning process. To this end, Arkwright adopted the Roving frame, in which the leading feature was again the celebrated drawing rollers. This machine made a soft and moderately twisted strand or roving, and if much twist had been put in, it would have refused to draw out finer at the spinning machine. Hence the means provided by Arkwright for the twisting and winding-on of the attenuated cotton on his spinning frame were utterly inadequate to cope with the soft loose roving, and as a matter of fact Arkwright never did see this problem satisfactorily solved.