ni 



HOROLOGY. 



BOROLOOY. 



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detcripUon. De \Vyck' clock wai regulated by balance in the 

 following manner (*g. 1) : The teeth of the crown-wheel E act on 



Fit- I. 



two small lever* F , called pallets which project from and form part 

 of an upright staff or spindle c n, on which is fixed the balance A n ; 

 and the mode of adjusting the clock to time was by shifting the two 

 weight* w w nearer to or farther from the centre. 



Although this clock of De \Vyck's, and indeed all those mode with 

 a balance for the regulator, without any regulation spring, must have 

 been very imperfect machines, we find that so early as 1484 AValtbcr, 

 and after him the landgrave of Hesse, made use of a balance-clock for 

 astronomical observations. Such, indeed, seems to have been the com- 

 parative utility of the clock thus early for astronomical purposes, that 

 Gemma Frisius proposed the use of a portable one for ascertaining the 

 longitude at sea about the year 1530. Ib 1560 Tycho Brahrf possessed 

 four clocks, which indicated hours, minutes, and seconds ; the largest 

 had but three wheels, the diameter of one of them being 3 feet, 

 and containing 1200 teeth, a proof of the imperfect state of clock- 

 work at that period. Tycho also observed irregularities hi his clocks 

 dependent upon changes in the atmosphere, but does not appear 

 to have been aware how they were produced. In 1577 Moestlin 

 had a clock which made 2528 beats in an hour, and by counting 

 the number of bents made during tho time of the sun's passage over 

 :dian, the sun's diameter was determined to be 34' 13". At 

 what time the size of clocks was reduced to a state of portability 

 is uncertain, but it must have been prior to 1514 ; for in ti. 

 the corporation of master clock-makers at Paris obtained from Francis I. 

 a statute in their favour, forbidding any one who was not an admitted 

 master to make clocks, watches, or alarms, large or small. Before 

 portable clocks could be made, the substitution of the main-spring for 

 a weight, as the moving power, must have taken place ; and this may 

 be considered a second era in horology, from which may be dated the 

 application of the fusee ; for these inventions completely altered the 

 form and principles of horological machines. 



Such was the state of clock-work when Galileo observed that heavy 

 bodies, suspended by strings of the same length, made their vibrations. 

 whether in long or short arcs, in very nearly, if not exactly, the same 

 spaces of time. Although he never applied the pendulum as a regu- 

 lator to supersede the balance in clocks, yet his discovery was the 

 prelude to n third era in clock-work, namely, the origin of the pen- 

 dulum clock. The honour of first applying the pendulum to a clock 

 has been a matter of much contention. Huyghens, whether the inventor 

 or not, undoubtedly applied it in the more masterly and scientific manner, 

 and hence has generally been considered the inventor ; but it is now 

 known that a London artist, named Kiehard Han-is, invented and 

 made a long-pendulum clock in 1641. Very soon after the application 

 of the pendulum to clocks, the idea of Gemma Frisius was attempted 

 to be realised by the ingenious Huyghi n in the construct!* n of a marine 

 clock, lie also discovered that its pendulum vibrated slower as it 

 approached the equator, which has led the way to a subsequent dis- 

 covery that the earth is not a globe, but on oblate spheroid. In 

 1676, Barlow, a London clockmaker, invented the repeating inn ' 

 by which the hour last struck may be known l>y pulling a 

 Several artiste followed in the same line, particularly Quart-, Julien 

 le Hoy, Collier, Lot-cay, and Thiout. t'lm-lc.s were soon after thin 

 made to show not only mean but apparent time. The principal artists 

 employed in this more curious than useful part of horology were Sully, 

 Father Alexander, Le Bon, Le lloy, Kriegseissen, Endcrlin,L' Adi . 

 Pawemont, Hivar, and Graham. The anchor escapement was tl 

 of Clement, a London clockmaker, in 1680. This change in the 

 escapement introduced the practice of suspending the pendulum by a 

 thin and flexible spring. The seconds' pendulum, with this eacapemcnt, 

 was called the royal pendulum. 



Another era in the history of clock-work conm ; n...l with the 

 beginning of the 18th century. In 1715 George Graham sought for a 

 i of rectifying the errors of the pendulum, caused by the 



traction and t xjnti.-ion of metals under changes of tein|xTaturo; and 

 this mean* he found in the celebrated mercurial j-einluliun. John 

 Harrison im].i..-...l on Craham's arrangement of the pendulum; and 

 Graham himself afterwards introduced his dead-beat ctca/xmcnl, as an 

 improvement on the anchor or recoil escapeinrnt pn-\ioii-]y in i : . . 

 From the days of Graham and Harrison sucecanive improvements have 

 been introduced in every part of the art. Such of those as are of 

 primary importance will be noticed as we proceed. 



Ckronomtttn. A chronometer, an eight-day spring clock, a tim< 

 piece, and a pocket watch have this hi common, that their source 



of power is derived from a coiled ipring, and not from a pendulum. 

 Chronnmetent are in extensive use for determining the longitude at 

 nea, and for other purposes where an accurate measure of time U 

 required, combined with great porUbilitv in the intniment. The 

 general appearance of what is termed a pocket chronometer is that of a 

 . ..minim watch ; and it is generally made to go the same time with 

 once winding up- namely, thirty hours. Thoee used for nautical pur- 

 pose! are larger, having dial-plates from three to four inches in 

 diameter, and are usually made to go from two to eight days between 

 the time* of winding up ; they have, in addition to the hour, minute, 

 and second circles, one on which a hand denotee the time in day* that 

 the piece has been going since the last winding up. Each chronometer 

 in well secured in a brass box, mounted on gimbals, in order that the 

 machine may preserve one uniform position, and is inclosed in a maho- 

 



A chronometer has for its moving power a main-spring, the variable 

 force of which is equalised or rendered uniform by tin- introdii. 

 the fiurt, a very beautiful contrivance. This fusee is a variable lever, 

 upon which the main-spring acts through the medium of the chain. 

 It is a mathematical curve which has this peculiar property, that 

 as the chain winds upon it, the distance from the centre 

 the fusee to the scmidiameter of the chain which is in eontvt with it 

 continually varies. The variation is in this proportion,- namely, that 

 the distance from the centre of motion of the fusee to the emi- 

 diimeter of the chain at that ]M.mt where it leaves the fuse* for the 

 barrel, multiplied by the force of the main-spring acting on the chain 

 at that time, shall be a constant quantity ; that is, shall be the same 

 whatever point of the fnree may be taken. Thus, at any given distance 

 from the centre of motion of the fusee, its power to turn any machinery 

 is uniformly ,md as the great or main wheel. liidi commu- 



nicates motion to all the rest, is attached to the fusee, their centres at 

 motion coinciding with each other, it follows that the power at the 

 teeth of the main wheel is perfectly uniform: this power is trans- 

 mitted through the medium of a train of wheels and pinions till it 

 comes to the escapement. 



A chronometer differs from a common watch in the escapement, and 

 in having a compensation for heat and cold. The peculiar mode of 

 effecting this compensation consists in having what is technically 

 termed an expatuion balance. The /</. 2 and 8 represent each a 



Fig. 2 



balance, some being mad" with weights, w W, as in fig. 2 ; others 

 with screws, as in tiy. 3. Kaeh consists mainly of two segments, and 

 each segment is of steel on the concave fide and of brass on the 

 convex; a steel bar, A, unites them. When such an apparatn 

 use, any increase of temperature diminishes the elastic force of the 

 balance-spring, which would cause the machine to lose ; but the same 

 degree of heat expands the outer rim of the balance, which is brass, 

 more than it does the inner one, which ig steel. Not being able to 

 separate, a curvature of the whole aim takes place, which carries tho 

 weight w towards the centre, whereby the inertia of the balance is so 

 much lessened as to allow t lie lialancc-spring to exert the same influence 

 as it ha i to the change of temperature. Again, a dimr 



of temjiorature increases the elasticity of the spring, which 

 cause the machine to gain ; but the bran contracting more than the 

 steel, produces a curvature of the arm outwards, which increases the 

 inertia of the balance, and allows the spring no more influence 

 than it hod previous t<i the change of temperature. The i 

 situations of the weights w w arc found by experiments on the rate of 

 the machine. U is evident that the nearer the weights are to the 

 moveable endu n a of the arms, the greater will bo the space through 

 which they move by any change of temperature, and consequently the 

 greater the variation in tho inertia of the balance; whence, if an 

 increase of t causes the machine to lose, or a decrease of 



causes it to gain, it shows tho compensation not to be 

 sutlii ii ntly active. In adjusting those balances made with screws, 

 it will readily be perceived that the moving in or out the screws 4 4 

 will produce a greater cflV.t than 3 ,'t, and theee again greater than 

 2 -', and no on; and, also, that in the adjustment two opposite screws 

 must always be moved in or out the same quantity. The mean 

 screws c C con produce no effect on the compensation, as no motion is 

 given to them by the curvature of the arms. It has been found by 

 experiment, that in every balance-spring of sufficient length, there is a 

 part of it which will be isochronal, or nearly to; and this length 



