Phthfopbical Ufes of * cemmon IVatch^ 5r 



ber of wheels and pinions, which are known by the fame names, and placed, no matter how 

 varioufly, fo as to aft together without interruption j but all watches have not their corref- 

 ponding wheels and pinions divided into the fame number of teeth and fpaces, and to this 

 circumftance it is entirely owing that the beats of different watches differ from each other. As . 

 the rate of going of a watch is regulated by the lengthening or (hortening of a fpring, without 

 any regard being paid to the numbers which compofe the teeth of the wheels and pinions, a 

 great latitude is allowable in the calculation of thofe numbers ; of which the different makers 

 avail themfelves according as the numbers on the engines they ufe for cutting the teeth re- 

 quire : but whatever the numbers may be of which the wheelwork confifts, if we divide 

 double the produ6l of all the wheels, from the centre wheel to the crown wheel inclufively, 

 by the produ<3: of all the pinions with which they adl, the quotient will be invariably the num- 

 ber of beats of the watch in queftion in one hour ; and again, if we divide this quotient hy 

 3600, the number of feconds in an hour, this latter quotient will be the number of beats in 

 every fecond, which may be carried to any number of places in decimals, and be copied upon 

 the watch paper for infpeftion whenever it may be wanted. 



When any particular watch is cleaned, the workman may be direfted to count, and return 

 in writing, the numbers of the centre wheel, the third wheel, the contrate wheel, and the 

 crown (balance) wheel, and alfo of the three pinions which they a£tuate, refpedlively, from 

 which the calculation of the length of a beat is eafily made by the rule juft given, and when ^ 

 once made will apply in all inflances where that individual watch is ufed. It will be remarked - 

 here, that no notice is taken of the wheels and pinions which conftitute the dial-work, nor yet 

 of the great wheel znd pinion with which it afts : the ufe of the former of thefe Is only to- 

 make the hour and minute hands revolve in their refpeftive times, and may or may not be. the. ^ 

 faine in all watches ; and the ufe of the latter, the great wheel and its pinion, is to determine, 

 in conjunftion with the number of ipirals on the fufee, the number of hours that the watch 

 ihall continue to go, at one winding up of the chain round the barrel of the main (pring : all 

 thefe wheels and pinions therefore, it will be perceived, are unneceffary to be taken into the 

 account in calculating the beats per hour. The reafon why double the product of the wheels 

 fpecihed is taken in the calculation is this, that one ^tooth of the crown wheel completely 

 elcapes the palats at every two beats or vibrations of the balance. A few examples will . 

 render the general rule perfeftly intelligible. Let us take for the firft example the numbers oif , 

 a common watch given by Mr. Emeribn in his '• Tradts," which, according to his method of 

 arrangement, ftand thus, 



48 great wheel, 



lai 5 4 centre wheel 



6 I 4 8 third wheel 



6 »■■ 48 contrate wheel 



crown whed 

 2 palats. 



H i \ Now, 



