Close one end of a piece of No. 2 tubing as described above, but leave the end somewhat pointed (1, Fig. 32). Heat the tube on one side at a distance ½ inch from the end and blow a bulb about ½ inch in diameter (2). Heat the tube ¼ inch from the bulb, draw it down into a fine tube, and break off the tube, leaving a small hole in the end (3). Place the submarine in a glass of water, and if it floats it is complete. Experiment 20. Magic. [Illustration: FIG. 33 THE SUBMARINE SUBMERGES ] Fill a bottle to overflowing with water, insert the submarine open end down, insert the solid rubber stopper and press down hard (Fig. 33). Does the submarine submerge? Release the stopper. Does the submarine rise and does it also move forward? Turn the bottle on its side and release the stopper quickly. Does the submarine shoot forward at a great rate (Fig. 34)? The submarine acts in this magical manner for the reasons given in Experiment 9. When you press the stopper in, you compress the air in the submarine and force water in until the submarine weighs more than an equal volume of water and it sinks. When you release the pressure on the stopper, the compressed air forces the water out until the submarine becomes lighter than an equal volume of water and it rises. The water rushing out through the opening exerts pressure backward on the water in the bottle and the reaction drives the submarine forward. Experiment 21. Fun with the submarine. If your friends do not know about the little submarine, you can mystify them as follows: Tell them that submarines are just like other fish; namely, they lay eggs, and the little eggs hatch out after a certain number of days (of course, your friends will know that you are only joking). Pretend that you found one of these submarine eggs, hatched it out in lukewarm water, and that you have trained the baby submarine to do some simple tricks. For example, that you have trained it to submerge, rise, and attack, when you issue the commands “submerge,” “rise,” and “attack.” [Illustration: FIG. 34 THE SUBMARINE SHOOTS FORWARD ] Tell them to watch the submarine carefully and to notice that it takes in water and submerges when you issue the command “submerge.” Stand the bottle on the table, issue the command “submerge” and, while your friends are watching the submarine, press down on the stopper unknown to them. [Illustration: FIG. 35 A SUBMARINE BATTLE ] Tell them to watch the submarine carefully again and to notice that it expels water and rises when you issue the command “rise.” Issue the command and unknown to them release the pressure on the stopper slowly. Repeat with the command “attack” and release the pressure quickly. Experiment 22. A submarine battle. Make a second submarine, place it in a large bottle with the first submarine, turn the bottle on its side, and make the submarines manœuver by moving the stopper in and out. [Illustration: FIG. 36 FLARING A TUBE ]