| Roget's Spiral demonstrates that there is an attractive
force between two parallel wires carrying electric current in the same
direction. The wire is actually coiled in a helix and not in a spiral,
prompting the alternative name of Contracting Helix. A pointed iron bob
on the end of the helix dips into a pool of mercury, and the upper end
of the helix and the mercury are connected to a source of EMF. The current
through the helix causes it to contract, breaking the circuit and removing
the force between the turns. The bob then falls into the mercury and the
cycle starts once more.
The helix at the right is from Vassar College, and on the left from the Smithsonian Institution.
| The Vassar instrument at the left was made by the L. E. Knott
Apparatus Company of Boston and cost $1.35 in 1916.
At the right is a Roget's Spiral from the early part of the twentieth century on display at the University of Cincinnati physics department.
On another page is the Roget's Spiral made by Daniel Davis that I use in demonstration lectures at Kenyon College.
||This example is at the University of Texas in Austin. It is unmarked, but is probably not made by Queen, as was much of the early Texas apparatus. The date is ca. 1900.|