In order to save time, the spindles move more rapidly during the process of stretching.

The mechanism by which this is effected is called double speed. The yarn being sufficiently hard twisted, the machine disengages itself from the other moving parts of the mule; the attendant then returns the carriage home to the rollers. By this arrangement, comprising the advantages Doth of the rollers and the spindles, the thread is stretched more gently and equally, and a much finer quality of yarn can therefore be produced. This excellent machine, which has superseded the jenny, and, to a considerable extent, the water frame, and which has carried the cotton manufacture to a perfection it could not otherwise have attained, was invented by Samuel Crompton, a young weaver of respectable character and moderate circumstances, living at Hall - in-the-Wood, near Bolton, and was completed by him in 1779. Being of a retiring and unambitious disposition he took out no patent, and only regretted that public curiosity would not allow him " to enjoy his little invention to himself in his garret," and to earn by his own manual labour, undisturbed, the fruits of his ingenuity and perseverance. The very superior quality of his yarn, it is said, drew persons from all quarters, to ascertain the manner whereby he produced it. He stated to Mr. Bannatyne, that, on the invention of his machine, he obtained 14s. per lb. for the spinning and preparation of No. 40, (i. e. yarn of forty hanks to the pound); that a short time after he got 25s. per lb. for the spinning and preparation of No. 60; and that he then spun a small quantity of No. 80, to show that it was not impossible, as was supposed, to spin yarn of so fine a grist, and for the spinning and preparation of this he got 42s. per lb.! These prices were obtained by the unrivalled excellence of the yarn; and it affords a criterion to estimate the value of the machine, when it is found that the price of yarn, No. 100, is at the present day only from 2s. 3d. to 3s. per lb., including the cost of the raw material, which is from lOd. to 1s. per lb., this surprising reduction having been effected chiefly by the powers of the mule; and notwithstanding it was before supposed to be impossible to spin 80 hanks to the pound, as many as 350 hanks to the pound have since been spun, each hank measuring 840 yards, and forming together a thread 1(57 miles in length! Although the principle of Crompton's machine was excellent, it was rudely constructed; his rollers were of wood, and all the parts clumsy; for Crompton was unused to tools, and knew but little of mechanics before he attempted to put to practice the beautiful combinations he had conceived.

His first machine contained but 20 or 30 spindles. Subsequently, Stones, of Harwich, a machinist, constructed a mule in a workmanlike manner, making the rollers of metal, and applying clock-work to move them; the mule was thus adapted for 100 to 130 spindles. Baker, of Bury, and Hargraves, of Toddington, introduced some improvements. In 1790, Mr. Kelly, of Lanark mills, applied water power to the mule, and shortly after Mr. Wright, of Manchester, constructed a double mule. By these successive additions the machine was made capable of working with no less than 400 spindles. Since this period mules have been so much increased in size and effectiveness, that there are many at work in Manchester and elsewhere of 800 spindles each, and some of the prodigious number of 1100 spindles each, or 2200 the pair, the pair being managed by one spinner. Mr. Crompton having made no attempt to secure this important invention, Parliament was memorialized on the subject, and a grant of 5000f. was obtained free of all charges; and it is worthy of remark, that at this time (1812), there were at work, on the principle of his invention, between four and five millions of spindles! But the course of improvement has not yet stopped; mules are now constructed which do not require the aid of a spinner, the mechanism being so contrived as to roll the spindle carriage out and in at the proper speed, without a hand touching it; and the only manual labour employed in these machines, (which are called self-acting mules,) is that of the children who join the broken threads.

The first machine of this nature was invented by the ingenious Mr. W. Strutt, of Derby, son of Mr. Jedediah Strutt, the partner of Arkwright. This appears to have been in the year 1790; and two years afterwards, Mr. Kelly, of Lanark mills, invented another self-acting mule, which is thus described by him in a letter to Mr. Kennedy, which we annex, as it furnishes a very interesting detail of the progress of improvement. "l first applied water power to the common mules in the year 1790; that is, we drove the mules by water, but put them up (that is, the carriage or spindle frame) in the common way, by applying the hand to the fly-wheel, and by placing the wheels (or mules) right and left; the spinner was thereby enabled to spin two mules in place of one.....The mules at that time were generally driven with ropes, made with cotton mill-waste, from a lying shaft in the middle of the room, and over gallows-pulleys above the fly-wheels, on each side of the room. That mode of driving was succeeded by belts, which were in every respect much better, and better adapted to self-acting mules, etc. From the above date l constantly had in view the self-acting mule, and trying to bring it into use; and having got it to do very well for coarse numbers, l took out the patent in the summer of 1792.

The object then was to spin with young people, like the water twist. For that purpose it was necessary that the carriage should be put up without the necessity of applying the hand to the fly-wheel. At first we used them completely self-acting in all the motions, the fly continuing to revolve, and after receiving the full quantity of twist, the spindles stood, the guide or faller was turned down on the inside of the spindles, and the points were cleared of the thread at the same instant, by the rising of a guide, or inside faller (if it might be so called). When the outside guide wire, or faller, was moved round, or turned down to a certain point on the inside of the spindles, it then disengaged, or rather allowed a pulley, driven from the back of the belt-pulley, to come into geer, or action, and which gave motion to the spindles, and took in the carriages at the same time (similar to the way you assist the large mules in putting up). But in the above self-acting mule, which performed every motion, after the spindles were stopped it required about three turns of the fly-wheel to move round the faller, and put in action the above-mentioned pulley that took in the carriage, which was a great loss of time.