The Tannerin is a musical instrument that is played by sliding a marker along the length of a wire or pad. This produces a pure sine wave tone, which can extend over as many notes or octaves as you wish, always in a smooth (i.e. portamento/pitch bend) fashion. It was used on the Beach Boys hit, "Good Vibrations."
With everybody building light theremins at the moment (myself included) I thought I'd better release an Instructable for the Tannerin.
Step 1: The Base
Begin by building the longest base possible. When sat in the middle, you should be able to easily reach either end. I built mine from Lego - just because I can. Then stretch a piece of nichrome wire across the entire width, and finish up by tying each end around a screw. This will help dissipate any heat that it gives off. Keep this wire taught. Measure the resistance of this stretch of wire, as this will give you an idea as the range, and granularity, of the instrument. Mine was 176 ohms, across 1.2 meters.