The gain in weight gives
the silver deposited.

To find the current in amperes, this weight, expressed in grammes,
must be divided by the number of seconds during which the current has
been passed, and by 0.001118.

The result will be the time average of the current, if during the
interval the current has varied.

In determining by this method the constant of an instrument the
current should be kept as nearly constant as possible, and the
readings of the instrument taken at frequent observed intervals of
time. These observations give a curve from which the reading
corresponding to the mean current (time average of the current) can be
found. The current, as calculated by the voltameter, corresponds to
this reading.

* * * * *

THE TWO OR THREE PHASE ALTERNATING CURRENT SYSTEMS.

By CARL HERING.

The occasion of the transmission of power from Lauffen to Frankfort
has brought to the notice of the profession more than ever before the
two or three phase alternating current system, described as early as
1887-88 by various electricians, among whom are Tesla, Bradley,
Haselwander and others. As to who first invented it, we have nothing
to say here, but though known for some years it has not until quite
recently been of any great importance in practice.

Within the last few years, however, Mr. M. Von Dolivo-Dobrowolsky,
electrical engineer of the Allgemeine Elektricitats Gesellschaft, of
Berlin, has occupied himself with these currents. His success with
motors run with such currents was the origin of the present great
transmission of power exhibit at Frankfort, the greatest transmission
ever attempted. His investigation in this new sphere, and his ability
to master the subject from a theoretical or mathematical standpoint,
has led him to find the objections, the theoretically best conditions,
etc. This, together with his ingenuity, has led him to devise an
entirely new and very ingenious modification, which will no doubt have
a very great effect on the development of alternating current motors.

It is doubtless well known that if, as in Fig. 1, a Gramme ring
armature is connected to leads at four points as shown and a magnet is
revolved inside of it (or if the ring is revolved in a magnetic field
and the current led off by contact rings instead of a commutator),
there will be two alternating currents generated, which will differ
from each other in their phases only. When one is