Beppicker—On the Influence of Magnetism on the Rate of a Chronometer. 5 
been produced by some extraordinary cause, not commonly operating on board 
ship.” : 
A suggestion as to what this ‘‘ extraordinary cause” may be, we find in his 
second Paper (No. 14), lying in the question—‘“‘ Is it not probable, or at least 
possible, that what Mr. Fisher has attributed to an unusual acceleration in the ship 
was actually a corresponding retardation on shore, occasioned by the action of 
some terrestrial magnetic power below the surface of the earth of Fair Haven ?”’ 
Such partial magnetic power is by no means rare. He adds some instances which 
have been communicated to him by very reliable observers. Captains. Vidal and 
Mudge found the coast of St. Mayo (Cape de Verd Island) so magnetic, that the 
needle of their theodolite became perfectly useless. If the chronometers, Barlow 
~ remarks, had been rated on St. Mayo, one certainly would have found very 
different rates from those on board, and, since the observations are able to show 
the differences only, one would have attributed these changes naturally to the 
action of the ship. Thus, if the chronometers had lost on shore, one would have 
assumed an acceleration on board. This mistake, of course, would have been 
discovered upon rating the chronometers again in London; and it is much to be 
regretted that Fisher does not say whether this was done in his case, or whether 
the chronometers were allowed to run down as usual at the end of the expedition. 
The three following instances Barlow gives all concur in showing remarkable cases 
of a local action on the compass needle, generally observed on approaching the 
coast. With this may be compared the note of W. Mudge (No. 3) as to the 
magnetic influence of the islands of St. Mayo and the Great Salvage. 
Fisher’s observations are, certainly, most striking; and Barlow is right in 
finding the greatest difficulty in the general acceleration of a// the chronometers. 
This is so much the more surprising when we compare these observations with 
those by Mudge, detailed above, where a tendency to lose was unmistakable. The 
explanation of the fact is by no means easy, though it is difficult to think of 
anything but magnetism. It is to be regretted that there is no special information 
as to the temperature, which, in spite of Fisher’s remark, may have been of 
considerable influence; and also that he does not give a list of the London rates, 
by which alone an opinion as to the relative value and trustworthiness of the 
second Table could be formed. Barlow’s suggestion is very ingenious, but its 
truth or value depends entirely upon observations to be made in Spitzbergen as to 
the local magnetic attraction, which, after all, does not seem to be so common as 
to justify such a supposition without proof. 
A few more instances may be briefly cited. Arnold and Dent (No. 17) 
frequently observed that the rates of very good chronometers in their workshop 
differed from their rates at the Royal Observatory by a constant amount of two or 
three seconds. They give the rates of three instruments in a small Table as 
follows :— 
