Thus in a given trade where there are several important processes, an improvement in one process which places it in front of the others stimulates invention in the latter, and each in its turn draws such inventive intelligence as is required to bring it into line with the most highly-developed process. Since the later inventions, with new knowledge and new power behind them, often overshoot the earlier ones, we have a certain law of oscillation in the several processes which maintains progress by means of the stimulus constantly applied by the most advanced process which "makes the pace." There is nothing mysterious in this. If one process remains behind in development each increment of inventive effort successfully applied there brings a higher remuneration than if applied to any of the more forward processes. So the movement is amenable to the ordinary law of "Supply and Demand" enforced by the usual economic motives. As the invention of the fly-shuttle gave weaving the advantage, more and more attention was concentrated upon the spinning processes and the jenny was evolved; the deficiency of the jenny in spinning warp evolved the water-frame, which for the first time liberated the cotton industry from dependence upon linen warp: the demand for finer and more uniform yarns stimulated the invention of the mule. These notable improvements in spinning machinery, with their minor appendages, placed spinning ahead of weaving, and stimulated the series of inventions embodied in the power-loom. The power-loom was found to be of comparatively little service until the earlier processes of dressing and sizing had been placed on a level of machine development by the efforts of Horrocks and others. Not until after 1841 was an equilibrium reached in the development of the leading processes. So likewise each notable advance in the machinery for the main processes has had the effect of bringing an increase of inventive energy to bear upon the minor and the subsidiary processes--bleaching, dyeing, printing, etc. Even now the early process of "ginning" has not been brought fully into line in spite of the prodigious efforts, made especially in the United States, to overcome the difficulties involved in this preparatory stage of the cotton industry.