HOROLOGY. 



137 



I'..-- -' i-*' 



(ion 

 co. 



PL.ITZ 

 IV. 



are turned fir?t on t!:r <tee and again on the brass, 

 after on the steel, are certainly very 



strong an ! ;;d nothing can well be said 



against them, and yet there appears to be a softness 

 ^h a balance that cannot exist in those where 

 the laminar are set or turned up by hand. There 

 a great deal more trouble in making 

 the last, and though it has been said that they cannot be 

 true or round when made in this way, yet we have 

 teen some of those done by Owen Robinson, as round 

 and true a* any turning could make them, and possess, 

 ing a degree of stiffness that cannot exist in the other : 

 they have been even unscrewed, or taken to pieces, and 

 again put together, without altering the rate of the 

 chronometer. After all we are not aware, that chrono- 

 meters with the one balance actually perform better 

 than tho*e with the other. 



..ay be observed, that on the rim of the turned 

 balances, which is separated into two, there are small 

 pieces of brass, made to slide backwards and forwards, 

 according as it may be found requisite, when under the 

 process of adjusting for heat and cold. In the other, this 

 is done by screwing backwards and forwards the pieces 

 of brass which turn spring-tight on small screws left at 

 the outer end of the laminar, and are bent in the same 

 with them. Both balances have what are called 

 meantime screw, placed in the vertical line of the hang- 

 ing position, which serve to adjust them to their rate of 

 time, \c- We hare seen and made compensation ba- 

 lances with three arms, and three pieces, and three 

 meantime screws, which were stiff, and answered very 

 welL 



CHAP. III. 

 OH Balance or I\nJutum Spring*. 



Tut invention and application of the spi al spring 

 to the balance of a watch, is by the fortign rtiU in ge- 

 oeraj ascribed to I Iu> gens, while they ' mit the kled of 

 a straight spring having been long before this applied 

 by Dr tlouke. It was in 1658 that Or Hooke ob- 

 served the restorative action of spring*, when he put 

 one to the balance of a watch, and applied for a patent 

 to secure hi* ri-..: >n- The profits were to 



b* divided between himself. Sir Robert Mora 

 Boyle, end Lord Braunckcr. It was not carru- ' 

 fleet, in consequence of a quarrel between the parties, 

 on account ol vt-ry unreasonable demand on the part 

 of these gentlemen. Nor was it till 107t that Fluy. 

 MM claimed the Mine discovery. Ilooke charged 

 tluygen* with plagiarism, through the intervention 

 of Sir Oldcnburgh, Secretary of the Royal Society, 

 who com i .11, when be was twice in 



land, the register* of the society , and also corresponded 

 with him upon toe ubj< 



ray reqaesta Oldenburgh to tell Huvgens that such 

 watches bed already been made .J, and to 



ask him if be does not apply a tpiral spring 

 balance arbor r It may be aiked, w litre had S 

 bert seen a spiral soring The natural answer is, that 

 he must have seen it in the hands of Ur I looke. 



On nothing does a chronometer depend so much as 

 in the good quality of the pendu' 



the power of the rudder is, in controuling and regu- 

 _ the motion of a ship, more extraordi- 



nary than that of this spring, in regulating Uc motions 



VOL. XI. PART I. 



Daliuicc 



of a chronometer, and we may be allowed to say, 

 that it possesses something like invitible properties. 

 It may be set so as to make the machine go fast or ' 

 slow, in anv position required, while neither its length, 

 nor the -weight of the balance, are in any way altered. 

 Le IV>y thought that he had made a great discovery, 

 and it must be granted to be one, when he found, Pr.ipertie. 

 " that there is in every spring of a sufficient extent, a ef bstaiee 

 certain length where all the vibrations, lone; or short, *'''" 

 great or small, are isochronous ; that this length being 

 found, if yon shorten the spring, the great vibrations 

 will be quicker than the small ones ; if, on the con- 

 trary, it fs lengthened, the small arcs will be perform- 

 ed in less time than the great ones." Notwithstanding 

 condition oftfffldemt extent, the isochronous proper- 

 ty will remain no longer than while the form of the spring 

 is preserved, an it originally was. Should the coils be 

 more compressed or taken in, the lonir vil<rations will 

 now be slower than the short ones ; and, on the con- 

 v more let out or extended, the long vi- 

 brations will I-- an the short ones. A more 

 general principle for obtaining the quality of isochron- 

 ism, may be applied, bv making the spring net propor- 

 tionally, in an arithmetical progression, according to its 

 tension. Fvery five degrees of tension should make 

 an equilibrium with a given force or weight, of ten 

 grains, that it, 5, 10, 1.5, 20, &c. degrees of tension, 

 should 1* Ujanced by 10. 20, SO, 40, tec. grain*. To 

 trjf small springs by this process would require a very 

 ntce and (Irliratc tool. ! l-t.-iin thr-r proper- 

 ties in pendulum prings tor hi* timekeepers, Hcrthoud 

 made them thicker gradually from the outer to the in- 

 ner er. : the reverse of this. 

 Whatever may be the form of the spring, whether flat 

 or cylindrical, the l>est and most direct way is to try 

 them in the timekeeper itself, by taking fmir hours go- 

 ing, with the greatest force the main spring can _ 

 ami thrn four hours with the lea>: It h of conse- 

 quence to have these springs hard, or well tempered. 



( HAP. IV. 

 On the Jetc riling of Pivot Holet. 



Ovn chronometers, from the art of jewelling the 

 pivot holes, may be said to have acquired a dur.il 



.aracter, which they would not have otherwise 

 received. It must not be imagined that there is any 

 time keeping principle or improvement in a jewelled 

 bole more than in a brass one ; and, notwithstanding 

 what has been said in favour of the last, few will l 

 hardy enough to run the hazard of having the balance, 

 and balance wheels, to move in brass holes. It is very 

 well known, that in a common verge watch, where 

 the balance holes are jewelled, its motion will IK- kept 

 up for a longer time than when it runs in brass holes. 

 '1 he friction at the balance holes cannot be supposed to 

 be less than at those of the fusee; for, in the time of 

 one-fourth of a turn of the fusee, the bal.-m. . 

 make more than what is equivalent to 9000 revolut 

 Berthoud regretted much that he had imt an i>|ij>ortu- 



t getting the pivot holes ol'hii time-keepers jew- 

 elled ; yet, from that versatility of genius which lie pos- 

 sessed, he supplied admiral)!;. t of this, in 



a manner that very few could have iquallid. Some of 

 the balances in his time-keepers were made to give six 

 s 





