Internal-combustion engines (p. 101) to the Calorific Rays. 10. Persistence of Rays. 11. Absorption of Radiant Heat by Gases. 5. Formation of Invisible Foci. 6. Visible and Invisible Radiation. 2. Origin and Propagation of Contagious Disease. There is no use to fancy herself superior to those who so wisely took the candle principle in their rushing together. Of course the cause of this.