Crompton, however, laid the foundation of the present system of mule spinning by combining the essential features of the two machines and blending them into one.
He applied the principle of roller drawing in order to first attenuate the cotton, and he utilised the travelling carriage as a reserve power with which to improve the quality of the thread and draw it out finer.
It must not be supposed that his travelling carriage was identical with that of Hargreaves. On the contrary, it was a vast improvement upon it. Crompton put the twisting spindles into the travelling carriage and the roving bobbins he transferred to a fixed creel, and these conditions are invariably to be found in the self-actor spinning mule of to-day.
In Hargreaves' machine the rovings were placed on the travelling carriage, and the twisting spindles in the fixed frame behind, a position which has never been acceptable since that time for cotton-spinning mules. Here, however, a word may be said in favour of Hargreaves' disposition of the parts mentioned. The Jenny did not contain any heavy drawing rollers and roller beams, and it was probably best in his machine to have his crude roving creel to traverse and the twisting spindles to be in a fixed frame.
This disposition of the parts is even now to be found in most Twiner Mules, that is, mules used to double two or more single threads together without any process of drawing being applied to the cotton.
When Crompton applied the principle of drawing rollers, his ingenious mind saw that it would be best to let the rollers, roller beam, and roving creel be in a fixed framework on account of their combined weight and size, making it very difficult to move them about.
Crompton's great idea seems to have been to produce a better thread by his machine than could be given by other machines, and in this he admirably succeeded.
The mule being set in motion, the rollers first attenuated and then delivered the cotton to the spindle carriage. The latter, by the action of the hand and knee, was made to recede from the rollers just about as fast as the cotton was delivered to the spindles, or possibly at a rather quicker rate. Then, while the thread was still in a soft state, the rollers could be stopped and the threads pulled still finer by the continued recession of the spindle carriage from the rollers. Afterwards, when that length of thread was fully made, it wound on the spindles, and the carriage at the same time returned to the roller beam.
Thus each portion of thread was first subjected to the action of drawing rollers, as in Arkwright's machine, and then drawn still finer by the withdrawal of the travelling carriage, as in Hargreaves' Jenny.
Shortly after Crompton's invention was given to the public, it began to be improved in various ways. Henry Stones, a mechanic of Horwich, near Bolton, substituted metal drawing rollers for Crompton's crude wooden rollers, doubtless copying the idea from Arkwright's water frame.