BeppickeEr—On the Influence of Magnetism on the Rate of a Chronometer. 45 
compass in the chronometer’s place on board ship was determined before the 
chronometer was installed on board (cf. p. 7). After the foregoing experiments 
of Delamarche and Ploix, it does not appear probable that, in the majority of 
cases, there would be very sensible differences of rate (cf. also pp. 22 and 28). 
Scoresby (No. 8) tried to avoid the influence of terrestrial magnetism (or rather 
the changes of this influence) by keeping the chronometer always in the same 
situation relative to the magnetic meridian. His contrivance, which is intended 
to serve this purpose, consisted of a thin plate (a compass card without a needle) 
connected with a compass needle at a distance of 5 inches, and suspended horizon- 
tally upon a point (with an agate cap), so that it was freely carried round by the 
magnetic needle. Thus, when a pocket chronometer was laid on the plate, it was 
obviously kept in the same position as to the magnetic meridian as long as the 
needle continued to traverse. If then the precaution was used to take the rate on 
shore while the chronometer was fixed in a certain position on this apparatus, there 
would be every chance of its maintaining its rate at sea, while the dip was nearly 
the same; “‘for the action of terrestrial magnetism, combined with that of the 
local attraction of the ship, would produce a mean action on the bar carrying the 
chronometer, and a similar action on the chronometer.” And further, he says :— 
“Under great changes, indeed, in the magnetic intensity or dip, a chronometer 
even thus situated might be liable to a small variation in its rate; but were the 
rate of the chronometer taken in various positions in the apparatus, and the position 
where its rate was nearest a mean given for its permanent position, then, I imagine, 
its rate would be uniform under all magnetic dips, and under all ordinary changes of 
intensity.” This apparatus (a drawing of which is given by Scoresby on his plate 
Xxill.) was found to answer very well. Scoresby was at first doubtful ‘ whether 
a. plate, however light, when loaded with the weight of a pocket chronometer, 
could be made to traverse by the polarity of only a compass-needle ; and whether, 
within a moderate compass, the magnet intended for directing the plate could be so 
far removed from the chronometer as to prevent all fear of additional mischief 
from its proximity.” But on trial it was found that the plate for the chronometer 
traversed when loaded with a pound weight avoirdupois, and that at 5 inches dis- 
tance the influence of the directing needle was only equal to the directing force of 
the earth on a horizontal needle in Britain. ‘‘ Now,” Scoresby continues, ‘such a 
degree of influence would probably be an advantage to the chronometer’s going 
rather than otherwise; because the denomination of magnetism in either end of 
the needle, operating on the part of the chronometer to which it was most con- 
tiguous, would be of the opposite kind to that of the earth operating on the same 
part of the chronometer ; hence the tendency of the magnetism of the needle on 
the chronometer (being the opposite of that of the earth, and nearly equivalent in 
intensity) would be to neutralize the effect of the magnetism of the earth on the 
chronometer.” If this remark holds good, it would obviously make the above 
