This is not the place to give a description of these two mechanisms, which can hardly be explained except with the assistance of purely technical drawings, but it may be remarked that weights are still the sole motive power of large clocks, and the escapement alluded to has been alone employed throughout the world until the end of the seventeenth century. Notwithstanding the importance of these two inventions, little use was made of them during the eleventh, twelfth, and thirteenth centuries. The water-clock and hour-glass (Fig. 144) continued exclusively in use. Some were ornamented and engraved with much taste; and they contributed to the decoration of apartments, as at present do our bronzes and clocks more or less costly. [Illustration: Fig. 144.--An Hour-glass of the Sixteenth Century,--French Work.] History does not inform us who was the inventor of the striking machinery; but it is at least averred that it existed at the commencement of the twelfth century. The first mention of it is found in the “Usages de l’Ordre de Cîteaux,” compiled about 1120. It is there prescribed to the sacristan so to regulate the clock, that it “sounds and awakens him before matins;” in another chapter the monk is ordered to prolong the lecture until “the clock strikes.” At first, in the monasteries, the monks took it in turn to watch, and warn the community of the hours for prayer; and, in the towns, there were night watchmen, who, moreover, were maintained in many places to announce in the streets the hour denoted by the clocks, the water-clocks, or the hour-glasses. The machinery for striking once invented, we do not find that horology had attained to any perfection before the end of the thirteenth century; but, in the commencement of the following it received its impulse, and the art from that time continued to progress.