delicate
weighing.

[Illustration: KENT'S TORSION BALANCE. Fig 4.]

The next step was the substitution of light forms stiffened by the wires
being tensioned over them. This was the invention of Professor Roeder,
recently deceased. The next step was the common counter scale, and then
that form of letter scale in which one of the bands acts as a fulcrum
and the other as a pivot.

After Professor Roeder's death, Dr. Alfred Springer, of Cincinnati,
continued perfecting this invention, and with marked success--scales not
intended for anything but the weighing of the ordinary articles of a
grocery store working so accurately that up to 50 lb. two grains would
turn the balance.

As will be noted, this balance dispenses entirely with knife edges, and
this statement carries with it the gist of its entire merit. There is no
friction, and the elegance of the work and the nice adjustments of the
parts struck the writer at once.

[Illustration: KENT'S TORSION BALANCE. Fig 5.]

The prescription scale and the proportional scale (see Fig. 4) are
particularly interesting. The former is sensitive to 1/64 of a grain,
and the latter, invented by Mr. Kent, is a most ingenious method for
weighing, by which, in a small compass (101/2 in. by 41/4 in. by 33/4 in.), we
have a balance capable of weighing 3 lb. avoirdupois by thirty-seconds
of an ounce.

For ordinary balances on the torsion system, in which extreme
sensitiveness is not needed, the trouble caused by change of level of
the scale is insignificant; but it becomes a matter of importance in
more sensitive scales, such as fine analytical balances in places where
it is impossible to keep the table or support of the scale level, for
instance on shipboard.

To counteract this effect of the change of level, Dr. Alfred Springer
devised the system which is shown in its most elementary form in Fig. 2.
An additional beam, E, with wire, F, and poise, H, on support, C, were
added to the balance, and connected to it by a jointed connecting piece,
J. The moment of the structure, E C H, about its center of rotation was
made equal to the moment of A C D about the center. The wires, B and F,
are attached at their ends to supports which are both rigidly connected
to the same base or foundation. If this base, the normal position of
which is horizontal, is tipped slightly, the weights, C and H, will both
tend to fall in the same direction. But suppose the right hand end of
the base is raised,