HOROLOGY. 
Fig. 7, represents the balance of a chrono- 
meter, or time-piece, as usually made by onr 
artists. A circular groove is turned in the 
flat face of a piece of steel, and into this 
groove a piece of good brass is driven, and 
a little of the solution of borax is applied 
to prevent oxydation. This compound 
piece being then put into a crucible; is 
made sufficiently hot to melt the brass ; 
which in these circumstances adheres firm- 
ly to the steel without requiring any solder. 
The face of the steel is then cleaned, 
and by proper application of the mecha- 
nical means of turning, boring, and filing, 
the superfluous steel is taken away, and the 
balance is left consisting of two or some- 
times three radii, and a rim, the external 
part of which is brass, and the internal 
part steel, the former metal being about 
twice the thickness of the latter. Some 
artists solder the metals together; and 
others plunge the steel balance into melted 
brass and suffer them to cool together, but 
the method we have described appears to 
be the best. In this state the arcs of the rim 
are then cut through and diminished in their 
length as in the figure ; and near that ex- 
tremity of each arc which is farthest from 
its radius, a piece or weight is put on, 
which can be slided along the arm so as to 
be adjusted at that distance, which upon 
trial shall be found to produce a good per- 
formance, under the different changes of 
temperature. For it scarcely need be ob- 
served, that the flexure of these arms by 
change of temperature, will carry the 
weights nearer to the centre, in hot than 
in cold weather ; and the more, the greater 
the distance of the weights from the radius. 
The small screws near the ends of the 
radii afford an adjustment for time ; as the 
balance will vibrate more quickly the fur- 
ther these are screwed in ; and the contrary 
will be the case if they be unscrewed or 
drawn further out. 
Fig. 8. shews a balance according to a 
construction used by Arnold, and specified 
by him to the commissioners of longitude. 
The expansion weights are cylindrical, and 
are adjusted upon the arm by screwing : 
and there is an inner rim upon which three 
weights are adjusted by sliding. These 
serve to regulate the going of the time- 
piece in different positions. 
If an uniform ring, with two or more 
radii placed at equal regular distances, and 
in all other respects alike, were to be 
poised on its axis, as a balance, no part 
would preponderate ; but it would remain 
at rest in any position ; and if we suppose 
the axis itself to be a spring, such as a piece 
of stretched wire, and we overlook the 
difference of tension in the wire, which 
might arise from the weight of the balance 
itself, iti different positions, it is obvious 
that all the vibrations of that balance, 
through equal arcs, would be performed in 
equal times, whether the balance were 
made to vibrate parallel to the horizon, or 
in any other position. But in the balance 
of a time piece, the pivots of its axis bear 
very differently, according to the position 
of the chronometer; and it requires some 
management to make the frictions the 
same, whether the axis be turning on one 
of its ends, or upon the two cylindrical 
faces of the pivots. And still more than 
this, since the balance itself has a perma- 
nent figure, compared with the spring, 
which in every part of the vibration alters 
its distance from the axis, and in every part 
of its length has a different degree ofrota- 
tary motion, it cannot be expected, nor does 
it happen, that a balance, which is found 
to be in poize, along with its spring, when 
out of the chronometer, will make equal 
vibration, as to time, in all positions when 
in its place. And in addition to these dif- 
ficulties, there is one part of the arc of 
vibration where the force of the spring, and 
the inertia of the balance, are not simply 
in opposition to each other, but are com- 
bined with the maintaining power ; namely, 
during the action of escape. The remedy 
for all these difficulties, which is happily 
adopted in thermometers for use at sea, is 
to place the axis in a vertical position ; by 
which means the balance itself is not affect- 
ed by gravity ; but for pocket time-pieces, 
the ingenuity of the artist is called upon 
for expedients, of which it would be not 
easy to exhibit a complete theory. The 
general principle commonly used, and also 
adopted by Arnold and Earnshaw, as far 
as can be gathered from the little they say 
in their specifications to the commissioners 
of longitude, is to , consider the balance, 
when out of adjustment for position, as a 
pendulum weight above and below the cen- 
tre of suspension, acted upon by gravity, — ■ 
and at the same time urged to a quiescent 
point by the force of elasticity. In these 
circumstances the vibrations will be qiiick- 
est when the point of stable equilibrium is 
downwards, and they will be slowest in the 
opposite position of the machine. This 
leads to the remedy of diminishing either 
the weight or the radius, on that side which 
