Summary: 1. A new experimental method of detecting pyro-electricity is given, which depends on the attraction between a charged crystal and a metallic conductor, the charge being developed by cooling the crystal in liquid air.

2. Results for a number of crystals are given, attention being drawn to dioptase, which although placed in a centro-symmetrical class, yet shows definite pyro-electricity.

3. A comparison is made between this and other methods.