Daniel Davis Jr. Separable Helices
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.
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.
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.
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
"Daniel Davis Jr. Manufacturer. Boston."



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