374 SURVEY OF THE COAST 



The delicacy of the scapement may be the cause why 

 English chronometers are very liable to momentaneous gains 

 or losses, which amount to a considerable number of seconds, 

 though in other respects they may be very good, and may 

 again return to their usual rate. It is probable that these may 

 be owing to some very slight motion which occurs just at the 

 moment when the scapement passes the stopping spring. 

 which then may either let the wheelwork, and of course the 

 hands, pass a number of seconds, or stop it for some time, 

 before it recovers its free and regular play, and rate of going. 

 This cannot be prevented in any voyage or journey. 



On the continent of Europe, a much smaller number of 

 chronometers is made, for the same reasons as stated in 

 respect to mathematical instruments. Only the most emi- 

 nent watchmakers engage in them, and they are, generally 

 speaking, as successful as the English. The principles upon 

 which they work are also different : but this is not the 

 place to enter into details on this subject. It is only proper 

 to mention that in case repairs, or even cleaning, should be 

 necessary in a chronometer, it can seldom be expected, that 

 any other chronometer maker will be able to do it so well 

 as he who has made the instrument, on account of his pecu- 

 liar mode of working. A like remark will apply with greater 

 force to English and French chronometer makers. 



1 should advise the use of no chronometers but such as go 

 only one day. All that go for a longer period have by no 

 means the same degree of accuracy. It is probable that one 

 of the causes of this arises from the too great influence of the 

 inequalities of the springs, which must of course extend over 

 a longer space of time. 



As it is well known that the principal difficulty in the di- 

 vision of mathematical instruments consists now in the pro- 

 per centring of the division with the axis of motion, it may 

 be proper to mention the manner in which this is effected, 

 and to give an idea of a dividing engine by which this error 

 may be avoided, and which 1 communicated to Mr. Trough- 

 ton. He approved of it so fully, that he advised Mr. The- 



