42 BeppickeEr—On the Influence of Magnetism on the Rate of a Chronometer. 
XII. 
[DELAMARCHE AND PLorx. ] 
The experiments of Delamarche and Ploix, the last that came to my know- 
ledge, were made with the practical view of ascertaining whether, and how far, 
the ship’s iron could have any influence upon a chronometer, or whether the in- 
fluence which a ship’s magnetism is known to exercise upon a compass would be 
sufficient to produce any sensible irregularity in the rate of a chronometer. 
Thus Delamarche and Ploix produced, by means of magnetic bars, a deviation 
of a compass-needle from 15° to 40°, which is the deviation observed in an iron 
vessel, and replaced afterwards the compass by a chronometer, in order to obtain 
in the changes of rate which might occur a measure for the action of the ship. 
These experiments were carried on during the time from June 1858 to January 
1859. The number of chronometers experimented upon was nine; the periods of 
exposure (or non-exposure) to the magnetic action were from five to ten days. The 
results are given in a Table (/. ¢., p. 264), which I reproduce. (See p. 43.) 
The conclusions drawn from this Table by Delamarche and Ploix run literally 
as follows :—‘‘ La colonne 5 de ce tableau donne les différences entre la moyenne 
des marches avant et apres l’épreuve et la moyenne des marches pendant ’épreuve. 
Ces différences, qui généralement ne sont que de quelques centitmes de seconde, 
quelles que soient les déviations produites, la position des barreaux, l’état des chro- 
nométtres et les circonstances extérieures de température on autres, nous semblent 
indiquer que l’état magnétique des batiments n’a pas d’influence sensible sur les 
marches des chronométres et qwil faut attribuer 4 d’autres causes les perturbations 
qui se manifestent dans ces instruments lorsqu’on les a transportés de terre 4 bord 
et réciproquement. 
‘“‘Les résultats de nos experiences sont dont contraires 4 Vopinion émise par 
quelques physiciens, opinion d’aprés laquelle le magnétisme pourrait determiner 
des variations de marches s’élevant & plusieurs secondes.” 
Now it is true that the above experiments show but very little effect upon 
the chronometers’ rates; it appears, however, probable that there is some—for 
instance in the first two experiments, where it is much to be regretted that the 
same arrangement of magnets (at first two, then a third compensating one) has not 
been applied alternately at different times. But it is very doubtful if Delamarche 
and Ploix’s conclusion is to be admitted as a general one; since after all the pre- 
ceding facts and observations, especially those of Barlow (p. 16 ff.), it is to be con- 
sidered highly probable that other instruments (perhaps with some fixed magnetism) 
would have shown more conspicuous effects. This shows how desirable it would 
