ding with the shutter open and
the plate ready for the exposure. Should a lightning streak appear
within the range of the lens it will be made on the plate, which
can be developed in the usual manner. It will require some
attention to that part of the sky within the range of the lens so
as to not make a double exposure by letting a second flash enter
the open lens.
--Contributed by Charles H. Wagner.

* * * * *

Borax may be used as a solvent for shellac gum.

* * * * *

** How to Make a Small Single-Phase Induction Motor [124]
By C. H. Bell

The following notes on a small single-phase induction motor,
without auxiliary phase, which the writer has made, may be of
interest to some of our readers, says the Model Engineer. The
problem to be solved was the construction of a motor large enough
to drive a sewing machine or very light lathe, to be supplied with
110-volt alternating current from a lighting circuit, and to
consume, if possible, no more current than a 16-cp. lamp. In
designing, it had to be borne in mind that, with the exception of
insulated wire, no special materials could be obtained.

[Illustration: Motor]

The principle of an induction motor is quite different from that
of the commutator motor. The winding of the armature, or "rotor,"
has no connection with the outside circuit, but the current is
induced in it by the action of the alternating current supplied to
the winding of the field-magnet, or "stator." Neither commutator
nor slip rings are required, and all sparking is avoided.
Unfortunately, this little machine is not self-starting, but a
slight pull on the belt just as the current is turned on is all
that is needed, and the motor rapidly gathers speed provided no
load is put on until it is in step with the alternations of the
supply. It then runs at constant speed whether given much or
little current, but stops if overloaded for more than a few
seconds.

The stator has four poles and is built up of pieces of sheet iron
used for stove pipes, which runs about 35 sheets to the inch. All
the pieces are alike and cut on the lines with the dimensions as
shown in Fig. 1, with the dotted line, C, to be filed out after
they are placed together. Each layer of four is placed with the
pointed ends of the pieces alternately to the right and left so as
to break joints as shown in Fig. 2. The laminations were carefully
built up on a board into which heavy wires had be