“Panuræ then took two glasses of the same size, filled them with water, and put one on one stool, and the other on another, about five feet apart, and placed the staff of a javelin about five-and-a-half feet long across, so that the ends of the staff just touched the brim of the glasses. That done, he took a stout piece of wood, and said to the others: “Gentlemen, this is how we shall conquer our enemies; for in the same way that I shall break this staff between these two glasses, without the glasses being broken or injured, or spilling a single drop of water, so shall we break the head of our Dipsodes, without any injury to ourselves, and without getting wounded. But that you may not think there is magic in it, you, Eusthenes, strike with this stick as hard as you can in the centre.” This Eusthenes did, and the staff broke in two pieces, without a drop of water being spilt. CHAPTER V. GASES AND LIQUIDS—PRESSURE OF THE AIR—EXPERIMENTS. We have more than once referred to the pressure of the air which exerts a great influence upon bodies in motion, but a few experiments will make this more obvious, and clearly demonstrate the fact. We have also told you some of the properties of Solids, such as Weight, Inertia, Friction, and Resistance, or Strength. Solids also, as we have seen, occupy space, and cannot be readily compressed, nor bent to other shapes. Now the subject of the Pressure of the Air leads us to the other forms of Matter; namely, Gases and Liquids, which will be found very interesting to study. [Illustration: Fig. 38.—Blowing an egg from one glass to another.] The force of air can very soon be shown as acting with considerable pressure upon an egg in a glass. By blowing in a claret glass containing a hard-boiled egg, it is possible to cause the egg to jump out of the glass; and with practice and strength of lungs it is not impossible to make it pass from one glass to another, as per illustration (fig. 38). The force of heated air ascending can also be ascertained by cutting up a card into a spiral, and holding it above the flame of a lamp (fig. 39). The spiral, if lightly poised, will turn round rapidly. Now let us turn to a few experiments with the air, which is composed in two gases, Oxygen and Nitrogen, of which we shall hear more when we come to CHEMISTRY. [Illustration: Fig. 39.—Movement of heated air.] [Illustration: Fig. 40.—Pressure of the air.]