CLOCK

instrument for measuring time, and showing on a dial hours, minutes, and sometimes also seconds. The earliest time-measurer was undoubtedly some form of sundial, in which the progre of the sun was registered by a shadow thrown upon a graduated plate. The sundial was followed by the Clepsydra, or water-clock, which measured the hours by the quantity of water discharged through a small hole in the containing ve el. The sand - gla worked on the same principle, sand or powdered eggshells taking the place of water, as in the familiar egg-boiler. The date of the invention of the clock proper is very uncertain, for the references to the early instruments of Boethius, Pacific us, and others are so vague as to leave it doubtful whether they were wheel-and-weight clocks or some form of water-clock. The earliest clock of which we have a full description was made in 1379 by a German named Henry de Wyck, and erected in Paris for Charles V. In this clock a cylinder was set in motion round {ts axis by the uncoiling of a cord carry-| ing a weight, this motion being ce ively communicated to a series toothed wheels, ending in the ment wheel. The teeth of the escape-| ment wheel acted upon two small called pallets, which projected from formed part of an upright spindle which was fixed the regulating balance. The cylinder also set in motion a to which was attached the hands of clock, The balance was loaded with weights, which resisted the unwinding of the cord, and the clock was regulated by increasing or decreasing the of the wights from the spindle. This struct i on formed the basis of practically all clocks up to the application of pendulum as a regulating power, was accomplished by Huygens 1657. The value of the poe regulating power lies in the fact that oscillations all take substantially the time, and after this date all clocks any z pretensions to accuracy were with a pendulum. The accuracy of pendulum as a regulator depends {ts being always the same length, with the simple pendulum serious errors arise from its expansion or contraction with variations in j temperature. obviate this defect, compensating penduant being the ‘gridiron’ an e ‘mercurlum, invented by Harrison in 1726, made of alternate bars of two different metals. When heated, one set expands upwards and the other downwards, the length of the bars are so proportioned a pee age mares sinners tarda the other. In rah am’s ‘mercurial’ pendulum, invented 1715, the bob sists of a gla cylinder containing cury. When a rise in temperature causes the metal rod to lengthen, the mercury simultaneously apr pas pDrans raising the center of inertia and counter acting the lengthening of the rod. Other great improvements Huygens’ clock were made, notably escapement, or mechanism which transforms the rotary wheel motion into oscillatory motion of the pendulum. Huygens’ clock required a light pendu proved arrangement, own as ‘crutch’ or ‘anchor’ escapement, was vented by Hooke about 1666. This vice allowed of a much heavier pendulum with smaller arcs of oscillation, is still largely used. Early in the XVIII. cent, an improved form known as ‘dead beat’ escapement was made Graham. This gives greater accuracy than the ‘crutch’ escapement, by obviating any recoil. Other escapements been invented to remedy small errors the previous forms, but these are used suc-|mainly in clocks for special purposes of| where absolute accuracy is required. In escape-|small portable clocks and watches, where the motive-power is a mainspring, levers | the motion is chiefly regulated by the and|escapement and _ balance-wheel, the on| gradual weakening of the motive force | as the spring uncoils being adjusted by a wheel | contrivance called the ‘fusee.’ The balthe | ance-wheel is compensated for variations two|in temperature on the principle of the | ‘gridiron’ pendulum. Various modifica- | tions of the escapement, in spring clocks distance|and watches have been introduced, con-| amongst which may be mentioned the the | escapements which are used in chronomabout}| oLopp EDW ARD (1840), En as 2| writer on folk-lore, myth, evolution, ’ etc.; g. its| twice president of the Folk-lore Soc.: same friend of George Meredith: has written with | Childhood of re Worlds igihe and fitted Dreams; OSton y of Primitive er agtarg Nan, Story of a the Alphabet, and -Antmiams id upon | Rom. politician; won notoriety for pene- | trating into mysteries of ‘Bona Dea’; To secured banishment of Cicero; became | a demagogue; killed in brawl with Milo. es pendu-}__CLOISTER was originally the general is|@me for an entire conventual building, | 21d in this sense is frequent in Eng. lit. Later applied to the covered ambulatory, and | the &% roof of which was supported * upon pillars and open arches, surrounding the quadrangle of a monastery, and here many of: the duties of a religious A house con-| Were carried on, (e.g.) copying and illumi- | The Cloisters of many Eng. cathedrals | 2re still in a perfect state of preservation, thus one of the finest examples being Glouces- | ter; winchester they are Schools, also to be ai seen tmme at sie Eton GF and the upon Oxford Colleges.