Smooth one end of a piece of No. 2 tube to put in your mouth, close the other end in the blowpipe flame, take it out and blow a bulb about 1/2 inch in diameter.

Allow the bulb to cool, then heat the tube about 1/4 inch from the bulb and draw it out into a thin tube. Now bend the thin tube at right angles near the bulb and break it off (Fig. 25).

Place the bulb in water. Does it float? If not, blow another with a larger bulb.

Fig. 25. A Pollywog

Experiment 13. Magic

Place the pollywog in a bottle filled to overflowing with water, insert the solid rubber stopper, and press it down hard. Does the pollywog sink?

Now release the stopper quickly. Does the pollywog turn somersaults in a most magical manner (1, Fig. 26), and also rise?

Make one or two more pollywogs, place them all in the bottle together (2, Fig.26), and entertain your friends with a pollywog circus.

The pollywog sinks when you press down on the stopper because you compress the air in it and force water in until it weighs more than the water it displaces.

The pollywog rises when you release the stopper be-cause the co impressed air drives the water out until the pollywog weighs less than the water it displaces.

The pollywog turns a somersault because the water rushes out sidewise in one direction and forces the nozzle in the other direction.

Fig. 26. Acrobats

Air may escape from the pollywog when it is turning a somersault ; if so, water will take its place, and may make the pollywog too heavy to float. You can restore its buoyancy by sucking out the water.

Experiment 14. A Dancing Pollywog

Make a pollywog as in Experiment 12, but bend its tail twice as shown in 1, Fig. 27; the nozzle is at one side and points sidewise.

Put it in the bottle full of water, then press down and release the stopper. Does it sink and rise, and does it also whirl around most beautifully as it rises?

Make another pollywog (2, Fig. 27), but bend its nozzle in the opposite direction. Does it whirl in a direction opposite to that of the first pollywog?

Put them in the bottle together and treat your friends to a pollywog dance.

The pollywog whirls because the water rushes out of the nozzle in one direction and forces the nozzle in the opposite direction.

Fig. 27. Dancing pollywogs

Drawing Glass Spider-Webs

Fig. 29. The Spider Trick