On the Trains of Watches. 4-7 



eligible number for the balance wheel, any one of the above pairs of wheels and pinions 



may be adopted, that the artift finds his other work will admit of: — what appears to me, 



on confidiring the fubjeft in a pradlical point of view, ds the moft eligible train, out of the 



64 60 60 X 15 X 2 

 many that have been fuggefted, is ~o~^ ~8~^ 6 ~^ 3600 = 5, which may be 



otherwife, perhaps more intelligibly, exprefled thus : 



64. Center wheel 

 Pin. 8 — 60 Third wheel 



Pin. 8 — 60 Contrate wheel 



Pin. 6 — 15 Balance wheel 

 2 Palettes. 

 Befides the advantage that this train, or one of a fimilar value, has over thofe before fpe- 

 cified, in point of producing a fteady equable motion, it has the further recommendation 

 of being capable of being counted decimally without any trouble ; for when any number of 

 beats are reduced into feconds by the divifor j, the remainder t/ottWi?(f will, in every in? 

 ftance, be fo many tenths of a fecond over, and will be an even or odd number, accord- 

 ingly as the termination of counting by the beats coincides with a beat, or falls in the in- 

 terval between two ; in the latter of which cafes there will be, befides the beats remaining 

 after divifioo, an half beat to be alfo doubled : thus, for example, in 132 beats of a watch, 

 which beats five times in a fecond. there are 26\ or 26,4 feconds, but in 132^ there are 



26 -^ or 26,5. 



When your readers confider what.expence has been incurred in improving watches by 

 the introduction of detached efcapements, compenfation balances, &c. whilft notwith- 

 Handing z fecond is the fmallefl portion of time they are hitherto intended to meafure, they, 

 will, doubtlefs, fee the propriety of making choice of fuch numbers in the confl;ru£lion of 

 thofe portable chronometers, as will not only tend to improve their rate of going, but will 

 render them, without any additional expence, capable of fubdividing the fecond into exadt 

 tenthsy and confequently of becoming admirably fubfervient to a great variety of philofo-- 

 phical refearches, in which a minute attention to time is indifpenfably neceflary. 



In a watch conftru£led to beat five times in a fecond, the main-fpring muft be fome- 

 what ftronger than in one which beats only four times, becaufe the contrate wheel, which 

 is a driver, has its diameter enlarged ; but what appears to me to be the greateft praftical. 

 objection to this conftrudlion, is that which applies to the deftrudtibility of the laft pinion }. 

 by a careful examination of the works of an old watch, it will appear,. that the pinions, 

 wear out before the wheels, and firft of all that pinion which is placed on the arbor or axis 

 of the balance wheel, by reafon of the number of its rotations :.on this account, partica- 

 larly where the ratio between the contrate wheel and pinion in queftion is fo high as 10 . 

 to I, the temper of the pinion ought to be well attended to, which is .ufualjy left iwfoft..h'<f. 



the J 



