The molecules of a heated body are in a state of active vibration. The motion of these vibrating molecules is communicated to the ether and transmitted by it, as waves, with wonderful velocity. Thus, when you hold your hand before a fire, the warmth that you feel is due to the impact of these ether-waves upon your skin; they throw the nerves into motion, just as sound-waves excite the auditory nerve, and the consciousness corresponding to this motion is what we popularly call warmth. Heat thus propagated by the ether, instead of by ordinary forms of matter, is Radiant Heat. The process of propagation is called radiation.