CHRONOMETERS. 109 



to, by our countryman Earnshaw, continue unrivalled : in fact they are generally 

 adopted by all intelligent chronometer-makers. 



We consider that the best balance is that composed of laminae of brass and steel, 

 when properly proportioned, and worked so that the particles are placed under no par- 

 ticular or partial constraint, which might prevent their free and natural action 

 througl out the whole periphery of the balance. This we consider an important 

 requisite ; for to the want of affinity in the condition of the particles, we attribute 

 some of the irregularities observed in the rates of chronometers, when subject to the 

 rigorous test of daily comparison — more particularly 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 theoiy, would be found in practice to answer so well. 



As evidence of our possessing means peculiar to ourselves, of bringing a chronometer 

 to keep a steady rate, we may mention the fact, amongst numerous other instances, and we 

 do it with much satisfaction, that of the eight chronometers entitled to the prizes for 

 the most accurate performance during the last three annual public trials at the Royal 

 Observatory, at Greenwich, _^ye were constructed by us, and adjusted on the principle 

 peculiar to ourselves. 



We may add, that within the last fifteen years, during which period 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 construction of the 

 balance-spring ; and the first performance of some of the instruments in which this 

 alteration was introduced, was 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 construction, with 

 a steel balance-spring, and which at the last public trial (1833) was second in per- 

 formance to one made by us, kept a remarkably 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. 

 Jour of which were made by us ; and the extreme variation of each, in the twelve 

 months, was considerably within the limits fixed in 1828 for the reward of Three Hun- 

 dred Pounds. Three of them made less error than our chronometer, No. 1410, in 1828 ; 



