BappickER—On the Influence of Magnetism on the Rate of a Chronometer. 41 
pre-occupation very well. He approached from above a magnet of moderate power 
to a chronometer of Jacob, which was not sensitive to temperature, and had a very 
uniform rate of + 15° to + 16° daily. The result was— 
11th January, rate + 155 gaining ‘‘ marche ordinaire.” 
12th : »» +386°2  ,, under the influence of the magnet. 
13th #5 » +76°4  ,, the first day after the removal of the 
magnet; and not until the 14th January did the rate again become + 15%5, and 
remain so. The interesting fact in this experiment, which deserves further observa- 
tion, viz., the continuation of acceleration after the removal of the magnet, Ansart- 
Deusy explains, according to his theory, by a repeated deformation of the spiral 
(once by the magnet and then by terrestrial magnetism). It is, of course, difficult to 
explain it satisfactorily from the few dates given; it is, however, probably an effect 
of the retentiveness of magnetization of the steel in balance and balance spring. 
Ansart-Deusy continues, that his not being acquainted with the position of the 
balance in the chronometer rendered it impossible to apply the magnet in the 
plane (!) of the spiral. He thinks, however, that there would have been no dis- 
turbance of rate, for then the deformation of the spiral would have taken place in 
its plane only, and, therefore, without any alteration of the length of its projection. 
This statement is the more extraordinary, as one look into the chronometer would 
have sufficed to show the situation of the balance ; and since Ansart-Deusy ought to 
have known from Fisher’s and Barlow’s experiments that a most considerable 
effect would have taken place—in fact that in Fisher’s experiments the effect 
of the magnet decreased when the magnet was not lying in the plane of the 
balance (page 14). 
Finally, Ansart-Deusy suggests as the place where a chronometer ought to be 
kept on board ship the point of intersection of the two axes of the ship’s induced 
magnetism, which are to be determined once with the vessel lying in the magnetic 
meridian and then at right angles to it. This rule, with which perhaps Givry’s* 
and Guépratte’s* are identical, does not take the ship’s permanent magnetism into 
account; its idea, however, to place the chronometer in the point of magnetic 
equilibrium is certainly well worth an experimental investigation, 
* Givry’s (No. 21) advice is to avoid the proximity of masses of iron, as well as too small a distance 
of the instruments inter se. This distance, he says, should not be less than two decimetres, ‘‘ pour 
éviter les choes et l’effet de l’attraction magnétique qu’elles pourraient exercer les unes sur les autres 
lorsqu’elles sous mises en mouvement.” Guépratte (quotation by Ansart-Deusy) says: “ On les 
installera vers le milieu du batiment, ol les mouvements sont moins sensible, de maniére de les garantir 
de Vinfluence magnétique des pitces de fer du batiment et des accidents imprévus.” 
TRANS. ROY. DUB. 80C., N.S. VOL. III. 
