Magnetism on Chronometers. 199 
same degree of intensity, the. acceleration or retardation produced 
by the action of the exciting force on one of the poles, will be en- 
tirely neutralized, by the opposite effects of the other. But if the 
attracting power be allowed to operate in a position nearer to one 
pole than the other, an alteration of rate will result from the change 
in the are of vibration, necessarily produced by the inequality of 
action. If on the other hand, the magnetic force be applied, in a 
direction between the thermometer-piece and time-screw belonging 
to the separate arcs of compensation, and having a polarity of a 
contrary kind to them, a constant effort will be made by the 
balance, to accommodate its arcs of vibration to the united effect 
produced by the maintaining power, and the intensity of the mag 
netic action; and a similar tendency will likewise be displayed by 
the balance, if the disturbing pole be placed: in the vicinity of a 
thermometer-piece and time-screw, having the same kind of po- 
larity with it. 
From the same considerations we may also infer, why a chrono- 
meter, having a balance powerfully magnetic, should present vari- 
ations of rate, from the influence of the earth alone, according as it 
is situated with respect to the magnetic meridian. If the thermo- 
meter-pieces alone are magnetic, and the line joining them be 
placed in any other direction than that of the magnetic meridian, a 
continual effort will be made by the balance to regain this position, 
thereby producing a change in the arc of vibration. Ifalso, the entire 
balance be considered as magnetic, some line may be found passing 
through its centre, in which it would repose in the direction of the 
magnetic meridian, if detached from the other chronometrical parts, 
and freely suspended. Hence it follows, that the moment the time- 
keeper is so placed, as to remove the balance from the Jast-men- 
tioned position, a tendency will be created in it, to return to that 
state; and which, by producing variations in the arc of vibration, 
must at the same time be accompanied by sensible alterations of 
rate. 
Having made these general observations, I shall finally consider 
the cause, why similar changes in the are of vibration, should be 
frequently attended, in different chronometers, with opposite alter- 
ations of rate, 
