Prof. Galileo Ferraris, of Turin, who has carefully studied
alternating currents and secondary transformers, has constructed a
little motor based upon an entirely new principle, which is as
follows: If we take two inductive fields developed by two bobbins, the
axes of which cut each other at right angles, and a pole placed at the
vertex of the angle, this pole will be subjected to the simultaneous
action of the two bobbins, and the resultant of the magnetic actions
will be represented in magnitude and direction by the diagonal of the
parallelogram, two consecutive sides of which have for their length
the intensity of the two fields, and for their direction the axes of
the two bobbins.
If into each of these bobbins we send alternating currents having
between one bobbin and the other a difference of phase of 90°, the
extremity of the resultant will describe a circle having for its
center the vertex of the right angle.
If, instead of a fixed pole, we use a metal cylinder movable on its
axis, we shall obtain a continuous rotatory motion of this part, and
the direction of the movement will change when we interchange the
difference of phase in the exciting currents. This rotatory movement
is not due to the Foucault currents, for the metal cylinder may
consist of plates of iron insulated from each other.
In order to realize the production of these fields, several means can
be employed: The current is sent from an alternating current machine
into the primary circuit of a transformer and thence into one of the
bobbins, the other being supplied by means of the secondary current of
the transformer. A resistance introduced into the circuit will produce
the required difference of phase, and the equality of the intensities
of the fields will be obtained by multiplying the number of turns of
the secondary wire on the bobbin. Moreover, 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._
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