causing both of the weights to tip to the left of
the vertical, D, tending to fall over, the left tends to raise the right
hand end of the beam, and the connecting piece, J H, also tending to
fall to the left, tends to lower the left hand end of E and the piece,
J. The moments of the structure, E C H, and A B D being equal, and one
tending to raise J and the other to lower it, the effect will be zero,
and J will remain in its normal position.

It is not at all necessary, however, to have the weights and dimensions
of the structure, E C H, equal to those of A B D. All that is necessary
is that the components of the weight of each part of the structure which
act vertically on J shall be equal and opposite. For, if the left end of
the beam, E, is made shorter than the right end of the beam, A, a given
angle of rotation of the beam, A, will cause a greater-angle of rotation
of E, consequently will tip the weight, H, further from the vertical
than the weight, D, is tipped, and in that case the weight, D, must be
made smaller than H, to produce an equal and opposite effect upon J. In
practice it is convenient to make the beam, E, only one-fifth to
one-twentieth as long as A, and to correspondingly reduce the weight, H,
relatively to D. In this case, on account of the angle of rotation of
the beam, E, being greater than the angle of rotation of A, the beam, E,
becomes a multiplier of the indications of the primary beam, A.

Mr. Kent has devised a modification of Dr. Springer's system, which is
shown in Fig. 3. It is applied in those varieties of the torsion balance
in which there are two parallel beams, connected by either four or six
wires. The wire, F, carrying the secondary beam, E, and poise, H,
instead of being carried on an independent support, rigidly attached to
the base, as above described, is attached directly to a moving part of
the balance itself, and preferably to the two beams. In Fig. 3, T T T
are trusses over which are tightly stretched the wires, B B B. A A' are
two beams rigidly clamped to the wires; _t_ is another truss with
stretched wire, F F. The upper wire, F', is attached by means of a
flexible spring and standard, S, to the upper beam, and the lower wire
is attached either directly or through a standard to the lower beam. The
secondary poise, H, is rigidly attached to the truss, _t_. The secondary
beam, E, is also rigidly attached to the truss, and acts as a
multiplying beam. The secondary structure th