The SAND-GLASS, as we have said, is an instrument of the same character as the Clepsydra,--the one measuring time by the fall of water and the other by the running of sand. Sand-glasses are known to have been used 200 B.C. The best hour-glasses, it is said, were those in which powdered egg-shells well dried in the oven were used instead of sand, such powder being less affected by changes in the atmosphere than sand would be. Sand-glasses are now seldom used except on board ship, and by domestics to compute the time for the boiling of eggs. King Alfred's invention for measuring time by the burning of candles, which were marked by circular lines to show the progress of the hours, was another effort of rude skill, which however could have been but partially successful even in the opinion of its inventor, for the accuracy of candle-horologes is interfered with by many different influences, prominent among which must of course have been the varying qualities of the materials used in their manufacture, and the more or less care with which they were guarded from the wind, so as to prevent their guttering. We now come to consider the date of the next grand step in the progress of Horology,--namely, that of the invention of the _clock_. The name itself may be derived either from the French, _la cloche_, a bell, or from the German, _die gloke_, or _die kloke_. There is no doubt that the word _cloche_ was meant to distinguish the instrument which marked the hours by sounding a bell, from the _montre_ or watch, which (derived from the Latin _monstro_, to show) merely shows the time by its hands. In ancient books the word _cloche_ simply stands for a bell,--the monks being accustomed to ring a bell at certain periods marked for them by their sun-dials or hour-glasses, and 'What's o'clock?' in old writers is often merely equivalent to the inquiry, 'What hour was last struck by bell?' The word horologe or hour-measurer of course equally applied to the sun-dial, the clepsydra, and the clock, and this convertibility of terms makes it all the more difficult to trace the point at which the newer invention began. Beckmann, in an ingenious analysis of various statements as to the first inventors of clocks made to go by weights and wheels, ascribes the invention to the eleventh century, but he does not attempt to name the first clockmaker. His authority for the date is the life of William Abbot of Hirshan, wherein there is mention made of a machine used by the monks for measuring time, which cannot in Beckmann's opinion have been a clepsydra. Beckmann does not believe that clocks were of European origin, but that they were derived from the Saracens. He founds his opinion upon a horologe described by Trithenius which was presented by the Sultan of Egypt in 1232, to the Emperor Frederic II. of Germany. 'In the same year,' says he, 'the Saladin of Egypt sent by his ambassadors, as a gift to Frederic II., a