WATCH. 



the fufee-engine accordingly as the adjufting-tool deter- 

 mines. The comparative forces of the fpring at the two 

 extreme ends of the fufee may be adjulled by the fmall 

 ratchet c, on the back of the pillar-plate in Jig. 7 ; but 

 when the fpring is put to a fuitable degree of tenfion to aft 

 well at both extremities of the fufee, it muft not be altered 

 by the ratchet-click, but the intermediate forces muft be 

 equalized by a due (hape given to the fufee. We have 

 inlifted the more on this part of the mechanifm bemg at- 

 tended to, becaufe, as the pr'mum mobile, it is the bafis of 

 all the other motions. The number of rounds that the 

 fpiral of the parabolic fufee may be cut into, depends on the 

 length of the pillars of the frame, or, which is the fame thing, 

 on \he fhallownefs of the watch. The French frequently 

 leave out the fufee, and attempt to equalize the forces of 

 the maiii-fpring by tapering it, and with detached efcape- 

 ments this mode may fometimes anfwer tolerably, but with 

 the crown-wheel efcapement a fufee is indifpenfable. Again, 

 the number of teeth in the great wheel, and in the centre 

 pinion, depends on the number of rounds in the fpiral of the 

 fufee ; in a 30 hours watch, with fix turns of the fufee, the 



great wheel muft have ^, or 5 times as many teeth as the 



centre pinion ; fo that if this has 6 leaves, the wheel muft 

 have 5x6 = 30 teeth ; but if 8, then 5 x 8 = 40 ; if the 

 fpiral has 7 turns, the great wheel 48, and the pinion 1 2, 



then the time of going will be -— x 7 = 28 hours ; alfo if 



there be j^ turns on the fufee, 50 teeth in the wheel, and 10 

 leaves in the pinion, the period of going will be 27^ hours^ 



or ^ X S\ — S ^ Si — ^'ih' ^"'^ 'f 24 hours only were 

 10 



required as the period, with 6 turns and a pinion of 12, the 

 great wheel would be required to have 48. Thus, when 

 an alteration is made in either the pinion, the wheel, or tlie 

 turns in the fufee, a correfponding variation may be made in 

 the others, to produce the fame period of going, but ftill 

 the centre-wheel revolves once in an hour. In the com- 

 moneft watches the pinions have only fix leaves each, which 

 do not aift fo well as pinions of higher numbers ; but in the 

 beft watches, and in all chronometers, the leaves and teeth 

 are more numerous. The pivot-holes, particularly of the 

 ▼erge and efcapement-wheel arbor, have jewels for the pur- 

 pofe of diminiftiing the fri£lion in the beft watches ; but 

 detached and remontoir cfcapements are the beft correftives 

 of the unequal impulfes given through the medium of the 

 train in the different ftates of its foulnefs. The potance m, 

 and fmall or counter potance n, that hold the pivots of the 

 balance-wheel, arc fmall cocks leen in Jig. 2. both in their 

 attached and detached ftates, and are fcrevved to the top or 

 upper plate within the frame, but the fprings, buttons, and 

 joints of the cafe are not exhibited, as forming no part of 

 the movement. Fig. 5. reprefents the outer face of the upper 

 plate, with the balance^, cock 0, and balance-fpring s, called 

 the pendulum-fpring, from its having the properties of the 

 pendulum ; by means of this fpring not only is the regula- 

 tion made fteady, but the adjuftment for time is effeiled. 

 In every balance-fpring there is a certain length, to be taken 

 as the effeftive length, by which the going of the watch, 

 to which it is applied, is limited to exaft performance, and 

 when this length is determined by experiment, a pin is put 

 in the ftud that holds the exterior end, as at 4, in Jg. 5, to 

 prevent its being altered ; but as the Tariation of tempera- 

 ture will alter the momentum of the moving balance, the 

 effeft thereby produced is a lofs of time, in the rate, in hot 



n 



weather, and a gain in cold, by an alternate increafe and 

 decreafe in the dimenfions of the balance itfelf, as well as by 

 fome alteration in the fpring : to remedy this defeft, in an 

 ordinary watch, the contrivance ftiewn in Jig. 6. is intro- 

 duced ; the wheel t is placed under the graduated circle r, 

 feen in^^. 5, and a circular rack a, Jig. 6, that holds the 

 curb or flit -piece 5, feen in both figures, is moved by a 

 Aiding motion given to it, when a key is applied to the 

 fquared arbor of the figured circle, and thus the eifeftive 

 length of the fpiral fpring is limited by the pofition of the 

 curb 5 ; and accordingly as the key is turned forwards or 

 back, towards the wordija/i or_/7oTf, engraved on the cock, 

 the ftiortened or lengthened fpring alters the rate of going, 

 till the proper length is found, that fuits the feafon in quef- 

 tion. In Harrifon's time-piece the curb was moved by an 

 expanfion-lever of two metals, that afted by means of the 

 change of temperature ; but in the beft chronometers of 

 more recent date, the compenfating levers conftitute the 

 three portions into which the rim of the balance is divided, 

 and the adjuftment for time, as well as compenfation for 

 temperature, are by means of heavy fcrews, which form a 

 part of the moving balance. In thefe more perfeft machines, 

 the length of the fpring, which is now made hehcal, or cylin- 

 drical, is firft determined fuch, that the long and (hort vibra- 

 tions are performed in the fame time, and this is called the 

 ifochronal length, which is not afterwards altered by fubfe- 

 quent adjuftments. But of thefe niceties we have treated 

 more fully under our long article Chronometer. The 

 laft portion of the watch, which demands our explanation, is 

 the dial-work, for producing the hours and minutes ; this 

 will be eafily underftood by a reference to figures 2 and 7 : 

 when the pinion, called the cannon-pinion, feen near the 

 minute-hand in Jg. 2, is inferted on the arbor of the hour or 

 centre-wheel, to which it fits rather tight by friftion, it re- 

 volves therewith in an hour, and receives the minute or long 

 hand on its protruding fquared end ; then this pinion drives 

 the wheel .v round a ftud on the pillar-plate, and with it a 

 pinion w made faft to its centre ; which pinion again drives 

 a fecond wheel "u round the tube of the cannon-pinion in 

 twelve hours, and to this the hour-hand is attached. This 

 diminution of twelve revolutions from the cannon-pinion to 

 the hour-wheel might be effefted by one pinion driving a 

 fingle wheel of twelve times its number of teeth ; but as the 

 motion muft be brought back to the centre of the dial again, 

 two more wheels, or a wheel and pinion, are neceiTary to be 

 introduced, and thefe are therefore made a part of the train, 

 and no large wheel or fmall pinion is wanted, for the ratio 

 1 2 : I may be more conveniently obtained by two faftors, 

 viz. 4 : I and 3:1; thus, fuppofe the cannon-pinion to 

 have 15 leaves, its wheel may have 4 x 15 = 60 teeth for 

 wheel .V, and if wheel v be made the fame its pinion will be 



360 



30 



60 

 3 



, , . 60 60 



20, and the tram — x — • 



15 20 



72 60 

 i- or — 

 6 5 



— or 1 2 ; fo that when the pinions are fixed upon for the 



dial-work, the wheels are readily determined, and vice verja. 

 Under our term CLOCK-Movement, we have given three 

 tables, containing the feveral varieties of the three diff^erent 

 portions of a clock-movement, which ai'e equally apphcable 

 to a watch -movement, and we prefume will be found ufeful 

 to the praftical workman, who is difpofed to vary his con- 

 ftruftion to fliew feconds, or for other particular purpofes.. 

 The following table, fomewhat differently arranged, was pub- 

 lilhed by W. Shirt, balance-wheel and fufee-cutter. No. 2J, 

 Coleman- ftreet, Bunhill-row, London, with which we will 

 conclude this divifion of our article. 



ATablb 



