r, the two bobbins may be
supplied by the secondary current of a transformer by producing the
difference of phase, as in the first case.

In the motor constructed by Prof. Ferraris the armature consisted of a
copper cylinder measuring 7 centimeters in diameter and 15 centimeters
in length, movable on its axis. The inductors were formed of two
groups of two bobbins. The bobbins which branched off from the primary
circuit of a Gaulard transformer, and were connected in series,
comprised 196 spirals with a resistance of 13 ohms; the bobbins
comprising the secondary circuit were coupled in parallel, and had 504
spirals with 3.43 ohms resistance. In order to produce the difference
of phase, a resistance of 17 ohms was introduced into the second
circuit, when the dynamo produced a current of 9 amperes with 80
inversions per second. Under these conditions the available work
measured on the axis of the motor was found for different speeds:
Revolutions per minute: 262--400--546--650--722--770. Watts measured
at the brake: 1.32--2.12--2.55--2.77--2.55--2.40. The maximum
rendering corresponds to a speed of rotation of 650 revolutions, and
Prof. Ferraris attributes the loss of work for higher speeds to the
vibrations to which the machine is exposed. At present the apparatus
is but a laboratory one.--_Bulletin International de l'Electricite._

* * * * *

THE ELECTRIC AGE.

By CHARLES CARLETON COFFIN.

The application of electricity for our convenience and comfort is one
of the marvels of the age. Never in the history of the world has there
been so rapid a development of an occult science. Prior to 1819 very
little was known in regard to magnetism and electricity. During that
year Oersted discovered that an electric current would deflect a
magnetic needle, thus showing that there was some relationship between
electric and magnetic force. A few months later, Arago and Sir Humphry
Davy, independently of each other, discovered that by coiling a wire
around a piece of iron, and passing an electric current through it,
the iron would possess for the time being all the properties of a
magnet. In 1825 William Sturgeon, of London, bent a piece of wire in
the form of the letter U, wound a second wire around it, and, upon
connecting it with a galvanic battery, discovered that the first wire
became magnetic, but lost its magnetic property the moment the battery
was disconnected. The idea of a telegrap