wire the more iron
will enter into the construction of the core, which is desirable.
Beginning half an inch from one end, No. 16 cotton-covered magnet
wire is wound from one end to the other evenly and then returned,
making two layers, and the terminals tied down to the core with
twine. Core and primary are then immersed in boiling paraffine wax
to which a small quantity of resin and beeswax has been added.
This same wax may be used later in sealing the completed coil into
a box. Over this primary is now wrapped one layer of okonite tape,
or same thickness of heavily shellacked muslin. This completed
primary will now allow of slipping into the hole in the secondary.

Should the secondary have been purchased without a case, a wooden
box of mahogany or oak is made, large enough to contain the
secondary and with an inch to spare all around, with room also for
a small condenser; but if it is not convenient to do this work, a
box like that shown in Fig. 2 may be purchased at a small cost. A
7/8-in. hole is bored in the center of one end, through which the
primary core projects 1/8 in. This core is to be used to attract
magnetically the iron head of a vibrating interrupter, which is an
important factor of the coil. This interrupter is shaped as in
Fig. 4, and is fastened to the box in such a way that the vibrator
hammer plays in front of the core and also that soldered
connections may be made inside the box with the screws used in
affixing the vibrator parts to the box. The condenser is made of
four strips of thin paper, 2 yd. long and 5 in. wide, and a
sufficient quantity of tinfoil. When cut and laid in one
continuous length, each piece of tin-foil must overlap the
adjoining piece a half inch, so as to form a continuous electrical
circuit. In shaping the condenser, one piece of the paper is laid
down, then the strip of tin-foil, then two strips of paper and
another layer of foil, and finally the fourth strip of paper. This
makes a condenser which may be folded, beginning at one end and
bending about 6 in. at a time. The condenser is next wrapped
securely with bands of paper or tape, and boiled in pure paraffine
wax for one hour, after which it is pressed under considerable
weight until firm and hard. One of the sheets of tin-foil is to
form one pole of the condenser, and the other sheet, which is
insulated from the first, forms the other pole or terminal. (This
condenser material is purchasable in long strips, ready for