On the Rates of Chronometers, 35 



magnetism on the rates of time-keepers; and secondly, as re- 

 spects the influence of that temporary degree of magnetism which 

 is communicated to iron generally, by induction from the earth. 

 Experiments on the former of these divisions have, however, been 

 by far the most numerous, in consequence, it may be presumed, 

 of the powerful effects it is capable of producing. But it may 

 be questioned, whether an inquiry into the alterations of rate pro- 

 duced by the action of induced magnetism, be not in reality, the 

 most useful and important of the two; and, though presenting 

 results of a less striking and remarkable character, deserves more 

 particularly to be investigated, on account of the greater analogy it 

 bears to the actual circumstances of a chronometer on shipboard. 



The magnetic influence developed by the iron of a ship, or what 

 is commonly termed its local attraction, owes its origin to induc- 

 tion from the earth. Its character is varied and uncertain in 

 some situations, unfolding its powers with .singular energy and 

 force ; whilst in others it either coincides in quantity with the 

 ordinary terrestrial intensity, or from the opposite and varied 

 directions in which the attractive forces act, exhibits an influence 

 very much below it ; agreeing in the whole system of its changes 

 with the alterations known to take place in the magnetic intensity 

 of masses of iron, when made to assume different positions, with 

 relation to the magnetic meridian. 



With such a perfect coincidence therefore between the local 

 attraction of a ship, and the induced magnetism of iron, it seems 

 difficult to account for the conclusions obtained by Mr. Fishbr* 

 and Mr. Barlow t, in their ingenious and valuable inquiries 

 respecting rates of chronometers ; the experiments of the former 

 leading us to infer, that the effects of iron on time-keepers is in 

 general to occasion an acceleration of their daily rates, and of the 

 latter, a retardation. 



Reasoning it priori, from our knowledge of the fact, that per- 

 manent magnetism sometimes accelerates, and at other times 

 retards the rate of a chronometer according to the direction in 



* Philosophical Transactions for 1820. 



t Philosophical Transactions for 1821. 



D2 



