Electric With the discovery of electricity and its development as a motive force, the horologists were among the first to attempt its use, as the ideal power to operate clocks. In the earlier devices the weight of the pendulum was changed from the usual vertical body to a horizontal form, provided with a coil, and caused to swing between two electro-magnets placed one above the other at the lowest point of the pendulum arc. Electri cal connections made and broken alternately by attachments to the pendulum stem actuated the magnets so as to attract the swinging weight as it approached the magnets and repel it after ter it had passed the centre. These impulses, how ever, were found in practice to be unmanage able, and quite inadequate to the task of keep ing the clock running uniformly. This idea was extended to comprise a row of electro magnets set in an arc close below the weight of the pendulum, the impulses of attraction ind repulsion being taken up consecutively by one magnet after the other. This device also proved impracticable. Another device experi mented with was the release by electrical action of a weighted bar, which in falling gave the stem of the pendulum a direct push. The bar was immediately pulled back to its normal position by an electromagnet, to be again re leased when the pendulum should begin to flag in its swing.
The so-called electric clocks of the present day are not time keepers but time transmitters. The actual measurement of time is made by a mechanical clock movement actuated by weights hanging from the barrel of a windlass—the centuries old and unrivalled °power° of the clock-maker. An electric current controlled by the clock mechanism is utilized to move the hands on a distant dial, or on several dials si multaneously — as in the case of tower clocks with four dials. Or it may be used to move the hands on the dials of many clock faces in a large establishment. Electricity is. also used in a similar manner to synchronise with a single master clock a series of individual clocks scat tered over a wide area. The devices for this kind of regulation generally act only upon the hands, forcibly moving them at stated inter vals into the exact position of the hands on the master clock. A common application of electricity to tower clocks is through a mechan ism known as the °waiting train." The auxili ary works which move the hands is speeded up slightly to cover a half minute (or some other period) in two or three seconds less than the exact time. The train of wheels is then halted by a catch which is thrown off by an electromagnet at the correct instant, and the auxiliary train resumes motion. Another adaptation of electricity to clocks is as a power to operate winding mechanism. To the wind
ing-post a revolving armature is attached, and switches are so arranged with trips that as the weights near the bottom of the run the cur rent is switched on and winding continues until the weights are at the top, when another trip throws the current off.
Tower Clocks.— Tower or turret clocks are to unusual stresses owing to their expose location as to wind pressures, and the fact that the very large and heavy hands are out in the open, unprotected from the weather, and so liable to be irregularly loaded with snow and sleet. The great difficulty of building a clock of sufficient power to overcome these varied stresses, while steadily pursuing its delicate task of measuring time accurately, led to the separation of the time keeping function from the time displaying mechanism, and con necting the two by an electric, pneumatic or hydraulic transmission. The clock mechanism proper may then be located in a room near the ground where it is not affected by the swaying of the tower by the wind. It may be driven by a comparatively light weight, and an auxili ary and independent train in the tower, run by a heavy weight, be merely controlled by the clock. The weight in the tower train may be entirely dispensed with, and the power operat ing the hands furnished by hydraulic pressure, or by compressed air, or by an electric motor train, released, in all cases, by delicate connec tions made or broken by the dock mechanism. These auxiliary power movements are generally arranged to operate pallets which impart direct motion to °escape wheels)) and thus connect with the usual wheel train to move the hands. The so-called "jumper clocks' are of this type, the half-minute or minute jumps being pro duced by a power impulse released by the master clock, acting on a ratchet-wheeL Bibliography.— Saunier, 'Treatise on Mod ern Horology in Theory and Practice) (trans. from the French by Tuppier and Rigg, London 1906); Kendall, 'History of Watches and Other Timekeepers) (London 1897); Grim thorpe, 'Rudimentary Treatise on Clocks, Watches and Bells) (London 1883); Britten, 'Old Clocks and Watches and Their Makers' (New York 1911) ; 'Watch and Clock Maker's Handbook, Dictionary and Guide) (London 1907); Goodrich, 'The Modern Clock' (Chicago 1905) ; Cunnynghame, 'Time and Clocks' (London 1906); Abbott, 'Amer ican Watchmaker and Jeweler) (Chicago 1910); and in the Journal of the Society of Arts (London, 7 March 1890) is an article on 'Recent Progress in British Watch and Clock Making.' The supplement of the Scientific American for 19 Sept. 1896 contains an article on 'Clocks Provided with Automotons); and The Electrician (London for 22 Dec. 1899), contains an article on 'The Electric Time Service.'