278. =Other Thermometers.=--Fahrenheit's thermometer is the one commonly used in this country. But there are several other thermometers on different scales, as the Centigrade, Reaumur's, and De Lisle's. In Fig. 195 you see the plans of the scales of these thermometers placed side by side. In the Centigrade thermometer, which is in use in France, and indeed in a large part of Europe, the zero, you see, is placed at the freezing point; and the space between this and the boiling point is divided into 100 degrees, which gives it the name Centigrade. Reaumur's, which is in use in Russia, has the same zero, but he has only 80 degrees from this to the boiling point. De Lisle's, which has gone entirely out of use, has its zero at the boiling point. The arrangement of Fahrenheit, although its zero is a mere arbitrary point, is, on the whole, the best, because its degrees are of such a size that they mark differences of temperature with sufficient minuteness for all practical purposes of an ordinary character without resorting to fractional parts. [Illustration: Fig. 196.] 279. =Expansion in Aeriform Substances.=--Heat produces a vastly greater expansive effect in air, the gases, and vapors, than it does in liquids. The expansion of air by heat may be shown very prettily in this way: Take a glass tube that has a bulb on one end, and, placing the other open end in water (as represented in Fig. 196), apply the palm of your hand to the bulb. The heat of the hand being communicated to the bulb will expand the air, and so, as you see, bubbles of air will escape through the water. On removing the hand, and allowing the bulb to cool, the air in it will be condensed, and water will pass up in the tube in proportion to the amount of air which has escaped. A bladder partly filled with air will be made to swell out to plumpness if it be heated sufficiently, and a full one may be so heated as to burst from the expansion of the air. Porous wood, as chestnut, snaps very much when burned, because the heat expands the air contained in the pores.