or small angles the sine and the arc are
practically equal.

When arranged as in Fig. 1, the scale is balanced only when the center
of gravity of the structure is vertically above the middle line of the
wire, and the support of the scale must be leveled in the direction of
the beam, so as to cause the center of gravity to take this normal
position. After the scale is thus leveled, if from any cause whatever,
such as shifting the scale on a table, or shifting the table itself, the
scale support is thrown out of level, the center of gravity of the poise
and beam is shifted from the vertical line above the support, and its
moment immediately becomes greater than the torsional resistance, and
the beam tips out of balance, and cannot be used as a correct scale
until the support is again leveled.

[Illustration: KENT'S TORSION BALANCE. Fig 2.]

In spite of all the foregoing facts, it was reserved for the
"Encyclopedia Britannica," in its ninth edition, to use the following as
the result of its condensed wisdom:

"In the torsion balance proper, the wire is stretched out horizontally,
and supports a beam so fixed that the wire passes through the center of
gravity. Hence the elasticity of the wire plays the same part as the
weight of the beam does in the common balance. An instrument of this
sort was invented by Ritchie, for the measurement of very small weights,
and for this purpose it may offer certain advantages; but clearly if it
were ever to be used for measuring larger weights, the beam would have
to be supported by knife edges and bearing, and in regard to such
applications therefore (as in serious gravimetric work), it has no
_raison d'etre."_

[Illustration: KENT'S TORSION BALANCE. Fig 3.]

This would seem to settle the whole case, for if the encyclopedia says
it has no reason to be, then, like the edict of the Mikado, it is as
good as dead, and if that is the case, "Why not say so?" On the
contrary, the torsion balance seems very much alive. But as it is not
very generally known, perhaps the early history of this form of balance,
briefly sketched, may prove of interest.

One of the first forms of the torsion balance which met the disapproval
of the "Encyclopedia Britannica" was attended with the difficulty that
the pivoted wires were attached directly to the bifurcated ends of the
beam, and could not be tensioned without bending these ends unless the
beam was made so heavy as to interfere with its employment in