TIMEKEE ITERS'. 55 



most elastic — then gold, and lastly, steel wire Eard drawn. 

 Springs composed of either the above substances, if the mate- 

 rials be good, will answer the purpose. The quantity of 

 copper alloy put to the gold, has been found to answer in the 

 proportion of from one eighth to a quarter, and many oiher 

 proportions may probably do as well. The form of the 

 spring is helical, or cylindrical, except for a portion of the 

 turn at each end, where it is curved in, and fastened at an 

 equal distance between its centre and circumference, see 

 Plate IL Fig. 2. Were not those turns to be curved inwards, —the' ends are 

 but left of the same diameter with the others, the spring 

 would not have its present easy, concentric motion, but on the 

 contrary, would jolt, wabble, and be distorted. Whether 

 the balance vibrates an arc of 230 degrees from its point of 

 rest in its forward direction, and re-vibrates 230 degrees 

 in its backward direction, making together 460 degrees, the 

 cylindrical figure of the spring is stili preserved. 



Upon the length of this spring depends the isochronism of Isochronism 

 the vibrations of the balance, and in every spring of 'a len-ilf " ^^ ^^^ 

 sufficient length, there is a place where all the vibrations, 

 long, short, and intermediate, will be performed in equal 

 times. 



When the timekeeper is first set goinsc, and always Semi-vjbra- 

 J. , , J. , . , . .** ^ , ,. / tions from ISO"* 



immcdTately after cleanmg and putting into good order j the to 250'\ 



main spring pulling with all its force, the oil applied to the 

 pivots clean and good, and every part performing its func- 

 tions to the greatest advantage; the balance may vibrate 

 from 180 to 230 degrees from the point of rest, according to 

 the power of the main spring, and the relative weight of the 

 ^balance. The balance also re-vibrates on the other side of 

 the point of rest nearly the same arc, but here we only 

 reckon the vibration on one side. 



From continual exertion, the main spring will undergo They fall off, 

 some diminution of its original power, and very great resist- 

 ance will be created from the thickening of the oil, tmd from 

 the accumulation of dirt, so that at the end of a long voyage, 

 suppose three or four years, the arc of vibration of the 

 balance will gradually decrease from 230 to probably 1 30 

 degrees, and so on, till in time it will come to rest. From 

 which it must be evident that if the diilerent arcs from 230 

 to 130 are not all performed in equal times, a great irregu- 



Vol. XIV.— May. i.806\ K arity 



