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This removable winding induced
current apparatus was made by Daniel Davis Jr.
and dates to 1840 - 1850. This was manufactured for educational purposes
and consists of a heavy gauge primary (inner winding) and a finer gauge
removable secondary winding. The base is mahogany and the layers of windings
are separated by newspapers. The original
binding posts are missing, the plugged holes for these can be seen at the
back edge of the coil base.The secondary winding (outer winding) is 10
-12 layers of about 234 turns/layer of 24 gauge (approximately)
wire. The secondary resistance is about 345 ohms. The
upper and lower brass caps on this winding are slotted. |
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The primary winding (inner winding)
is 2 layers of 114 turns/layer of 14 guage (approximately)
wire. The primary resistance is about .7 ohms. The primary is wound on
a slotted
(lengthwise) brass tube. |
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A picture from the 12th edition
of Davis's Manual of Magnetism, 1857.
The original "screw cups" are missing, as well as the "rasp" mounted in
front of the coil. |
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Another picture from the same
catalog, depicting one use for the coils. One pole of a battery would be
connected to point A and the wire connected to the other pole would be
dragged across the rasp. The person holding on to the metallic handles
would then feel "slight shocks" and slighlty stronger ones when the circuit
was broken. It is noted that "the intensity of the shock may be varied
at pleasure, by altering the number of iron wires, the addition of a single
wire producing a manifest effect." If the motion of the wire over the rasp
is quickened, "the arms are much convulsed; and if it is drawn over
rapidly, the succession of shocks becomes intolerably painful." For a complete
copy of this section of Davis's manual, click here. |
