TIME KEEPERS. 4^7 



gine, then you will have feven pair of pieces of equal fize 

 and weight ; two of tliefe pieces being fcrewed on the rim of 

 the balance at equal difJances will produce an equilibrium, a 

 balance in the full fenfe of (he word, equal in all its parts. 

 Jn making balances great care Hiouid be taken that they get 

 no bruifes or bendings, for if they get a bruife on one fide fo 

 as to indent the metal, that part will be lei's alfedled by heat 

 and cold than the other parts which have not received the 

 jame violence to clofe its pores. 



To adjuft the balance in heat and cold— put the watch into Adjuftment to 

 about 85 or 90 degrees of heat, by the common thermometer, tempemures' 

 mark down exadly how much it gains or lofes in 12 hours, 

 then put it into as fevere cold as you can get for 12 hours, and 

 if it gains one minute more in 12 hours in cold than in heat, 

 move the compenfation weights farther from the arm of the 

 balance about | of inch, and if it gains one minute more in 

 12 hours in heat than in cold move the weights y of inch 

 nearer to the arm of the balance, and fo on in the like pro- 

 portion, trying it again and again till you find the watch go the 

 iame in whatever change of heat or cold you put it. 



Much difficulty has fallen to the lot of watchmakers in the — ^nd in all 

 endeavour to make timekeepers go nearly the lame in the dif- ^^^ 

 ferent pofitions. I have had my (hare of this, but it is now 

 over ; by far the greateft part of this difficulty arifes from the 

 balance fpring not being properly made. But if the fpring is Rule. If the 

 made, as I (hall defcribe hereafter, you have only to make J^-^{^f^ wilUo 

 the balance of equal weight and it will go within a few fe- nearly alike in 

 conds per day in ail pofitions alike, and if it vibrates not more ^^ P"^-!'"!?* j_^ 

 than one circle and a ^, by applying a fmall matter of weight ding weight to 

 to that part of (he balance which is downward when in the '^^ loweit part 



_ . , ■ , r n -11 n ■ ■ ^ whCH in lofing 



poiition that it lofes molt, will cnrrea it wi^h great accuracy; pofition if the 

 but if it vibrates more than one circle and a ^, then it will fa"ic vibration 

 require the weight to be above infiead of below ; and after ;/ ^o^e degrees 

 the watch has been going a few mopths and its vibration then add to the 

 ihortens to one i circle, then it will go worfe and worfe by ^^''^'^ ^"^* ^^^ 

 reafon of the weight being in the wrong place ; therefore, to rate vibration i» 

 avoid this evil, it is abfolutely necelTary to confine the vibra- ^^** 

 tions to one ^ circle, which will produce the molt fieady per- 

 formance. It is common for watchmakers to adore a tiqie- 

 Iceeper when they fee it vibrate a circle and a half, or ipore, 

 and form an opinion of its excellence from this only ; but I 



know 



