Chronometers. 301 



ibr to the want of affinity in the condition of the particles, we attrib- 

 ute some of the irregularities observed in the rates of chronometers, 

 when subject to the rigorous test of daily comparison, more particular- 

 ly after sudden changes of temperature. There are inherent defects in 

 the shape of the balance, which prevent its affording theoretically 

 the means of a perfect compensation ; but it is doubtful whether 

 other forms, which appear preferable in theory, would be found in 

 practice to answer so well. 



As evidence of our possessing means pecuHar to ourselves, of 

 bringing a chronometer to keep a steady rate, we may mention the 

 fact, and we do it with much satisfaction, that of the eight chronom- 

 eters entitled to the prizes for the most accurate performance during 

 the last three annual public trials at the Royal Observatory, at 

 Greenwich, jive of those chronometers were constructed by us, and 

 adjusted on the 'principle peculiar to ourselves. 



We may add, that within the last fifteen years, during which peri- 

 od we have been adjusting our chronometers on this principle, 

 we have had extensive experience of its efficacy, having made and 

 sold more than twice as many marine chronometers as any other 

 maker has done during thirty years ; — the best proof that the public 

 have appreciated our discovery. 



Attempts have recently been made to introduce glass in the con- 

 struction of the balance-spring ; and the first performance of some 

 of the instruments in which this alteration was introduced, were very 

 satisfactory. 



There is, however, reason to apprehend that this material will 

 not be found to give to the instrument a permanent rate, as one of 

 the very best of them has, in the course of a few months, deviated 

 from its rate to the amount of seven seconds a day : while another 

 chronometer, under the same circumstances, on the usual construc- 

 tion, with a steel balance-spring, and which at the last public trial 

 (1833), was second in performance to one made by us, kept a re- 

 markably steady rate. 



We may also be allowed to state, that on this trial (1833), sixty 

 chronometers were sent by various makers ; and at the termination, 

 the numbers were reduced to ten, four of which were made by us ; 

 and the extreme variation of each, in the twelve months, was con- 

 siderably within the limits fixed in 1828 for the reward of Three 

 Hundred Pounds. Three of them made less error than our chro- 

 nometer, No. 1410, in 1828 ; for which we then received the premi- 



