The investigation of rod is measured by a micrometer screw. The brass tube is 50cms x 2.5cm C.P. With inlet and outlet tubes for steam and opening for thermometer reading to 1°x 110°C. The binding posts are provided on the supports for connecting a bell, buzzer or galvanometer for indicating the exact point of contact of the screw. Provided with three rods of brass, iron and aluminium without belland battery.

The apparatus consists of a clear perspex tube 250mm long x 50mm outside diameter provided with a light, freely sliding expanded polystyrene piston and a loose fitting metal cap.