ses. The speed of
the motor is 9,000 revolutions per minute, and the dynamo is driven
direct from it; at this speed it gives a current of 100 amperes with
and from 55 to 70 volts; the intensity of the light is from 5,500 to
6,000 carcels. The carriage upon which the whole of this apparatus is
mounted is carried on four wheels, made of wood with gun metal
mountings. These are more easy to repair when in service than if they
were wholly of iron. The weight of the carriage is three
tons.--_Engineering._

* * * * *

ELECTRIC MOTOR FOR ALTERNATING CURRENTS.

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 deg., 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. Moreove