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Diagram of Temperature. The Thermometer. Comparative Scales.Nature of Heat. Natural and Artificial Temperatures. Heat of Caloric is that principle in nature, by the action of which fluids are evaporated, and solids are either dissipated in vapour, rendered fluid, or vitrified. "Heat," as Dr. Lardner remarks, "is one of the physical agencies upon which the well-being of organised nature in general, and of the human race in particular, is most essentially dependent...Upon this principle the theometric barometer is constructed, which indicates the elevation of any place above the level of the sea, by the difference in the heat required to make water boil at that elevation. Thus water boils at the top of Mont Blanc at 187°. Effects of Heat. Measured by Daniell's Pyrometer. Greatest furnace heat measured by Daniell...For measuring temperatures below the freezing point of mercury a spirit thermometer is used, alcohol not congealing by any reduction of temperature hitherto observed. For measuring high temperatures, above those indicated by the thermometer instruments called Pyrometers are employed, these are various forms , and act upon the principle of the expansion of metals by heat.