Made of varnished wood with glass front and membrane suspended on cord for loading with sand to show positions of nodes and antinodes, overall length 760 mm.

Comprising a wooden resonance box of 114 cm., length, 12.5 cm. width and 10 cm. height, with two rules 1 meter long sub-divided into millimeters. One each brass and steel wire of different diameter attached to fixed bridge and tensioned by fine adjustment pets, two movable bridges, pulley and fixed screw to enable a third wire to be fixed for tensioning by masses. One each additional wire of steel and brass, each 1.5 mm. length and 22 swg.

This is a modern version of the apparatus originally designed to show the effects of vibrations in a stretched cord, and investigate the relationship between frequency, tension and density. In addition the provision of electrical contacts, opened and closed by the'vibrating armature, allow the apparatus to be used as high speed changeover switch in, for example, capacitor charge/discharge experiments. Comprises a thin steel rod armature, mounted in a clamp formed by a pair of 4 mm. socket terminals, so that its free length may be adjusted as desired. An AC. energising coil surrounds the armature and a permanent magnet provides the necessary magnetic polarisation. The free end of the armature equipped with a small boss and clamping screw for attachment of the cord and also serves as the moving contact when the apparatus is operating as a changeover switch. A pair of 'fixed' contacts are positioned either side of the armature, these also being adjustable for optimum position in their 4 mm.' socket terminal support clamps. The complete apparatus is carried upon a box type base.