| Another name for Roget's
Spiral is the Contracting Helix, and this is how Davis lists it in the
1851 Manual of Magnetism, pp 233-234. He wrote: "The mutual
attraction between different portions of the same current moving in the
same manner, may be rendered evident by the instrument[s represented here].
A wire, coiled into a loose helix, is supported in a vertical position by
a brass pillar connected with one of the screw-cups on the base board. The
lower end of the helix dips into mercury contained in a glass cup with a
metal bottom, by means of which the mercury is brought into connection with
the other screw-cup.
When the battery is applied, the portions of the current traversing the
The apparatus at the left is one which I have used for many years at Kenyon College, and on the right is a contracting helix at Washington and Jefferson College. These examples are unmarked, but have the brass ball feet of Davis apparatus. Davis priced the item at $3.50.