The effects of temperature and pressure on the thermal conductivities of bodies. Part I.–The effect of temperature on the thermal conductivities of some electrical insulators.

The substance whose thermal conductivity is to be determined has the form of a cylinder about 8 cms. long, 2 cms. diameter, and is surrounded by a thin cylinder of brass, which on account of its comparatively high thermal conductivity, makes the outer surfaces of the substance isothermal surfaces. The brass cylinder is placed in a Dewar The heat is supplied by the passage of an electrical current through platinoid wire embedded in the substance parallel to the axis of the cylinder, and about .4 cm. distant from it. The amount of heat generated is determined by the current through the wire and the potential difference between its ends. The temperature is measured by the electrical resistance of two short spirals of No. 40 pure platinum wire, down the centre of one of which the heating wire passes. To eliminate errors due to want of symmetry, a second heating wire passes down the centre of the second spiral, and the heating current may be sent through either or both at will.