The pendulum and watch-springs needed to have their movements controlled and balanced by better escapements. Huygens thought that the pendulum should be long and swing in a cycloidal course, but Dr. Hooke found the better way to produce perfect isochronous movements was to cause the pendulum to swing in short arcs, which he accomplished by his invention of the anchor escapement. The fusee which Dr. Hooke re-invented consists of a conical spirally-grooved pulley, around which a chain is wound, and which is connected at one end to a barrel, in which the main actuating spring is tightly coiled. The fusee is thus interposed between the wheel train and the spring to equalise the power of the latter. To Dr. Hooke must also be credited the invention of that delicate but efficient device, the hair-spring balance for watches. His inventions in this line were directed to the best means of utilising and controlling the force of springs, his motto being “_ut tensio sic vis_,” (as the tension is so is the force.) Repeating watches to strike the hours, half-hours and quarters, made their appearance in the seventeenth century. In the next century Arnold made one for George III., as small as an English sixpence. This repeated the hours, halves and quarters, and in it for the first time in the art a jewel was used as a bearing for the arbors, and this particular one was a ruby made into a minute cylinder. After the discovery and practical application of weights, springs, wheels, levers and escapements to time mechanisms, subsequent inventions, numerous as they have been, have consisted chiefly, not in the discovery of new principles, but in new methods in the application of old ones. Prior to the eighteenth century, however, clocks were cumbrous and expensive, and the watches rightly regarded as costly toys; and as to their accuracy in time-measuring, the cheaper ones were hardly as satisfactory as the ancient sun-dials. With the coming of the machine inventions and the new industrial and social ideas of the eighteenth century came an almost sudden new appreciation of the value of time. Hours, minutes and seconds began to be carefully prized, both by the trades and professions, and the demand from the common people for accurate time records became great. This demand it has been the office of the nineteenth century to supply, and to place clocks and watches within the reach of the poor as well as the rich. While thus lessening the cost of time-keepers their value has been enhanced by increasing their accuracy and durability. Among the other ideas for which the eighteenth century was famous in watch-making was that of dispensing with the key for winding, thus saving the losing of keys and preventing access of dust, an idea which, however, was perfected only in the last half of the nineteenth century.