CHRONOMETERS. 107 



even assigned the period when the cure might be expected to be completed : but time 

 being no party to the bargain, generally left the instruments thus turned over to its 

 benevolence to pursue their vagaries without interference. 



The cause, which the writer alluded to has assigned for this acceleration, is the use of 

 tempered balance-springs; now tempered balance-springs have been in use for more 

 than half a century, and forty years ago they were made by ourselves. If time, there- 

 fore, could have cured the defects of the tempered balance-spring, as stated in the 

 paper above alluded to, these old chronometers would now have been excellent instru- 

 ments, which certainly they are not in general found to be. 



The consequence has been, that the rates of most of the chronometers at this 

 moment in existence, can only be considered constant for short intervals of time. 

 Many years have elapsed since our attention was drawn to this peculiarity, from 

 several mortifying circumstances which occurred in our own experience ; and after 

 satisfying ourselves that it was in vain to look for the cause of so perplexing a phe- 

 nomenon in the 7nechanical construction of the instrument, we resolved to examine the 

 physical condition of the materials of which the balance and its spring are made : and 

 we discovei-ed that the greater part, if not the whole of the discrepances, were owing 

 to circumstances in this physical condition. 



After many experiments and much investigation, we had the good fortune to discover 

 the means of correcting this physical peculiarity, either completely, or so nearly, that 

 we can now undertake (after ascertaining the tendency) so to alter the physical pro- 

 perties of the balance and its spring, as to make any chronometer, whose mechanical 

 construction is otherwise satisfactory, perform with sufficient exactness for every purpose 

 for which chronometers ai'e generally required. 



The acceleration of chronometers on their rates, hitherto unexplained in the history 

 of chronometers, is produced by the constant action of winding and unwinding the 

 balance-spring, which, in chronometers beating half seconds, takes place two hundred 

 and forty times in each minute, and it is thereby deprived of a portion of its elasticity. 

 It becomes consequently stiffer, stronger, and more stubborn ; and as the motions of the 

 balance (the measurer of rime) are regulated by this spring, the vibrations become 

 more rapid, and are perfonned in less time. 



The cause of chronometers losing on their rates, is also generally to be traced to the 

 physical imperfection of the balance-and-spring ; which, contrary to what takes place in 

 the tempered spring, becomes relaxed by constant action, combined with other causes ; 

 and consequently has less power over the vibrations of the balance. But independently 

 of all accidental circumstances, the chronometer is continually changing its rate, with 

 every alteration of tension in the balance-spring. 



