108 CHRONOMETERS. 



The scientific artist may, indeed, give to this spring the isochronal property, so far 

 that under given and constant circumstances, unequal arcs of vibration in the balance, 

 will be performed in equal time; but this adjustment will in no degree counteract the 

 effect occasioned by change of tension to which we have been adverting. 



We do not allude in the preceding remarks to defective compensation 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 interferes with their usefulness. 



It is true that all chronometer makers do occasionally produce instruments, which, 

 for a sufficient length of time, keep steady rates ; but they do so only from accidental 

 circumstances, of which the makers themselves are not always aware. They ap- 

 proximate to the con-ection which we have discovered the means of making in all cases. 

 In our researches on this subject, we have found that the defect in the correction for 

 change of temperature, is amongst the least of the difficulties to be contended with ; 

 and the value of the principle of adjustment which we have discovered has been 

 eminently proved by the accurate performance of our chronometers, which have been 

 exposed to the severities of the arctic winters, in all the Polar voyages. In one of 

 those voyages, eleven out o{ Jifteen chronometers stopped from the cold ; whilst four 

 made by us, (all of ours that were sent) maintained the same rates at Melville island 

 that they were found to have in London after the return of the expedition. 



The chronometrical parts of our chronometers consisting of the compensation balance 

 and the detached escapement, are the same as invented before 1766, by the eminently 

 distinguished artist, M. Le Roy, of Paris, with the important improvement of the 

 detant on a spring instead of on pivots, as made by the late Mr. Earnshaw ; together 

 with some minor but useful alterations in the execution and arrangement suggested by 

 our own experience. 



We have said before, that chronometers made by the same artist do not always 

 perform equally well, although the same workmen are employed, the same labour is 

 bestowed, and the same attention paid to each. Several modern artists have endeavoured 

 to remedy this defect by means of mechanical contrivances, some of which display con- 

 siderable ingenuity and are apparently very plausible ; but, however beautiful in theory, 

 these contrivances have produced no practical advantage ; no one has yet discovered 

 the seat of the disease, or the cause of so remarkable an effect. We reassert that 

 no mechanical contrivance can remedy the defect : it is only to be remedied by a know- 

 ledge of the principle which we have discovered. 



Le Roy's original inventions of the balance for compensating for changes of 

 temperature, and the escapement, were entitled, from their beautiful simplicity, to 

 the reward so justly bestowed upon him ; and with the improvement above alluded 



