If your friends do not know about the little submarine, you -an mystify them as follows: Tell them that submarines are just like other fish; namely, they 1 a y 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."
Fig. 33. The Submarine Submerges
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.
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.
Make a second submarine, place it in a large bottle with the first submarine, turn the bottle on its side, and make the submarines manceuver by moving the stopper in and out.
Fig. 35. A submarine battle
Finally arrange them so that they are on the bottom, facing each other bow to bow, two or three inches apart (1, Fig. 35), and release the stopper quickly. Do the submarines try to ram each other (2, Fig. 35) in a most realistic manner?