Chronometer's. 299 



the balance and its spring are made ; and we discovered that the 

 greater part if not the whole of the discrepances^ were owing to cir- 

 cumstances in this physical condition. 



After many experiments and much investigation, w^e bad the good 

 fortune to discover the means of correcting this physical peculiarity, 

 either completely, or so nearly, that w^e can now undertake (after as- 

 certaining the tendency) to alter its physical properties, and to make 

 ANY chronometer, whose mechanical construction is otherwise satis- 

 factory, perform with sufficient exactness for every purpose for which 

 chronometers are generally required. 



The acceleration of chronometers on their rates is produced by 

 the constant action of winding and unwinding the balance-spring, 

 which takes place two hundred and forty times in each minute, and 

 it Is thereby deprived of a portion of its elasticity. It becomes con- 

 sequently stifFer, stronger, and more stubborn ; and as the motions 

 of the balance (the measure of time) are regulated by this spring, the 

 vibrations become more rapid, and are performed in less time. 



The cause of chronometers losing on their rates, is generally to 

 be traced to the physical defect of the balance and spring; which, 

 contrary to what takes place In tempered spring, becomes relaxed by 

 constant action, combined with other causes, and consequently has 

 less powder over the vibrations of the balance. But independently 

 of all accidental circumstances, the chronometer is continually chang- 

 ing its rate, with every alteration of tension in the balance-spring. 



The scientific artist may, indeed, give to this spring the isochro- 

 iial property, so far that under given and constant circumstances, un- , 

 equal arcs of vibration In the balance, will be performed In equal 

 time; but this adjustment will in no degree counteract the effect oc- 

 casioned by change of tension to which w^e have been adverting. 



We do not allude in the preceding remarks to defective compen- 

 sation for change of temperature, but to that gradual deviation from 

 the rate which*^many chronometers are found to exhibit, and to an 

 extent that often inteferes with their usefulness. 



It is true that all chronometer makers do occasionally produce In- 

 struments, which, for a sufficient length of time, keep steady rates; 

 but they do so only from accidental circumstances, of which the ma- 

 kers themselves are not always aware. They approximate to the 

 correction which we have discovered the means of making in all 

 cases. 



