FIG. 64.—SECTION THROUGH PYROMETER. FIG. 65.—TWO FORMS OF LE CHATELIERe of a slightly varying composition, a heating of the junction of which produces a current of electricity proportioned to the degrees of heat applied. The amount of this current is measured by a suitably calibrated galvanometer, and thus we can read off the heat at any convenient distance rapidly and with a surprising degree of accuracy.