touches the hot iron at all, provided the heat is sufficiently intense, but assumes a slightly elliptical shape and is supported by a cushion of vapor. If, instead of a flat-iron, we use a concave metal disk about the size and shape of a watch crystal, some very interesting results may be obtained. If the temperature of the disk is at, or slightly above, the boiling point, water dropped on it from a medicine dropper will boil; but if the disk is heated to 340° F., the drop practically retains its roundness—becoming only slightly oblate—and does not boil. In fact the temperature never rises above 206° F., since the vapor is so rapidly evaporated from the surface of the drop that it forms the cushion just mentioned. By a careful manipulation of the dropper, the disk may be filled with water which, notwithstanding the intense heat, never reaches the boiling point. On the other hand, if boiling water be dropped on the superheated disk its temperature will immediately be reduced to six degrees below the boiling point; thus the hot metal really cools the water.
By taking advantage of the fact that dif-
