§ 7 Invisible Images Formed by Radiant Heat
Perhaps no experiment proves more conclusively the substantial identity of light and radiant heat, than the formation of invisible heat-images. Employing the mirror already used to raise the beam to its highest state of concentration, we obtain, as is well known, an inverted image of the carbon points, formed by the light rays at the focus. Cutting off the light by the ray-filter, and placing at the focus a thin sheet of platinized platinum, the invisible rays declare their presence and distribution, by stamping upon the platinum a white-hot image of the carbons. (See fig. 51.)