By the help of an iron-copper junction introduced into the smaller compression apparatus lately described to the Society, I have examined for a number of substances the rise of temperature produced by a sudden application of great pressure, and the corresponding fall of temperature when the pressure was very suddenly relaxed. The copper-iron circuit is, however, too little sensitive for very accurate measurements ; as, from the nature of the apparatus, the wires must be so thin as to have considerable resistance, and the thermoelectric power of the combination is not large.