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.
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