You boys who have the Gilbert set on “Hydraulic and Pneumatic Engineering” will know that it is the pressure of the atmosphere which causes the water to run up over the edge of the tumbler in this magical way. Experiment 33. A long-armed siphon. [Illustration: FIG. 47 SIPHONING WITH LONG TUBES ] Attach a full length of No. 4 tube to each arm of the siphon, as in Fig. 47, and repeat the experiments described above. =Note=: When you insert a glass tube into a rubber coupling or rubber stopper, wet the end of the glass tube and the inside of the coupling or stopper, grasp the tube near the end to be inserted, and insert with a twisting motion. Experiment 34. To make a nozzle. Attach a working handle to one end of a piece of No. 2 tube, heat the tube about one inch from the end in the lamp flame, turn constantly until soft, then remove from the flame, and draw it out about 3 inches. When cool, break off the thin tube, cut off the nozzle to a length of about 2½ inches, smooth the large end, and your nozzle (Fig. 48) is complete. Experiment 35. To make a fountain. Arrange the apparatus as in Fig. 49, and suck air out of the nozzle. Have you made a beautiful fountain? [Illustration: FIG. 48 A NOZZLE ] [Illustration: FIG. 49 FIG. 50 FIG. 51 FIG. 52 YOU MAKE A NUMBER OF MAGIC FOUNTAINS ] Experiment 36. Magic. Make a nozzle 6 inches long out of No. 2 tube. Smooth the ends of the nozzle, and long tubes. Arrange the apparatus as in Fig. 50 and suck air out of the nozzle until the water runs in the siphon. Does the water squirt out of the nozzle in a magical manner? Experiment 37. More magic. Arrange the No. 2 apparatus as in Fig. 51, with the nozzle inside the bottle. Now to start the apparatus: Fill the bottle about quarter full of water, insert the tubes in the stopper as shown; insert the stopper into the mouth of the bottle; invert the bottle; then put the short tube in a tumbler full of water and the long tube in an empty pail or basin. Is there a magical fountain inside the bottle? Repeat this with a taller bottle, if you can find one to fit your two-hole stopper. Do you get a higher fountain? Experiment 38. Still more magic. [Illustration: FIG. 53 STARTING A SIPHON ] Make another nozzle and attach it to the apparatus used in the last experiment by means of the inverted siphon (Fig. 52). Start the experiment as described above. Do you get two fountains? Experiment 39. To start a siphon. [Illustration: FIG. 54 SIPHONING SAND ] You can start a siphon without sucking the air out of it as follows: Fill the siphon with water, put a finger over each end (1, Fig. 53), place one end in a tumbler full of water and remove the finger under water (2, Fig. 53), then remove the other finger. Does the siphon start? In this case the water you pour into the siphon drives the air out, and this is the reason you do not need to suck the air out. Experiment 40. To siphon sand or mud.