44 Bappicker—On the Influence of Magnetism on the Rate of a Chronometer. 
be to carry on experiments like the above with chronometers of known magnetic 
qualities; but more will be said about this later on. Some features in the present 
experiments deserve attention, as the production of a special compass deviation, 
but otherwise they show a considerable want of systematic arrangement. And 
further, as the differences between the mean rates before and after the experi- 
ment are sometimes larger than the final values in the fifth column, the 
reliance to be put in the results becomes rather questionable. The following 
remark of Delamarche and Ploix shows, however, that this want of accuracy was 
not unintentional :—‘‘ Nous savons bien que ces expériences laissent & désirer sous le 
rapport de la précision, mais il nous a semblé que, pour le but que nous proposions, 
il était inutile de pousser plus loin l’exactitude. Nos recherches tendent seulement 
 indiquer de quel ordre sont les influences diverses auxquelles sont dues les varia- 
tions de marche des chronométres, afin d’attirer l’attention des horlogers en ce qui 
concerne la construction de ces instruments et celle des marins en ce qui concerne 
leur usage,” 
XIE: 
It remains now, before we proceed to discuss the best arrangement of chrono- 
metrical experiments, to review briefly the few suggestions made in order to avoid 
the magnetic influence upon a chronometer. As to the removal of iron out of 
the chronometer, and the destruction of magnetic intensity in the iron parts, we 
refer to the remarks on p. 11; and as to the proper placement of the chronometer 
on board ship, see p. 41. The rules of Shadwell (No. 28) are somewhat similar to 
Givry’s; he only recommends, in addition, to keep the XII—VI lines, in all 
chronometers, always in the same direction relative to the ‘ fore-and-aft”’ line 
of the vessel, in order to make an eventual magnetic influence aiiect all chrono- 
meters similarly. There are also to be considered the suggestions of Barlow, 
Scoresby, and Airy. 
Barlow (No. 6) thinks it possible to determine, beforehand, a ‘ship’s rate,”* 
by observing the chronometer in the neighbourhood of a vertical iron disc, the 
influence of which is supposed to be equal to that of the ship’s iron. This method 
of representing the ship’s iron is now superseded; the idea of Barlow’s suggestion, 
however, deserves attention and an experimental trial. This could, perhaps, be 
arranged, if a list of the rates was furnished (with the usual temperature list), 
which the chronometer would have for different degrees of deviation, produced 
in a compass standing in the place of the chronometer, and if the deviation of a 
* Peter Lecount (No. 7) (cf. p. 16) thinks it would be impossible to determine a sea-rate, on 
account of the considerable changes of the magnetic power and direction of the ship’s iron in 
different dips, 
