Place the lower tumbler on the book and the upper tumbler on the table. Does the water now run in the opposite direction until the levels are again the same?
Raise one tumbler a foot or so above the table. Does the water run up over the edge and drop into the second? Now before the upper tumbler is empty, lower it in such a way that an arm of the siphon is in each tumbler, and raise the second tumbler. Does the water now run in the opposite direction?
FIG. 46
THE WATER STOPS WHEN LEVELS ARE THE SAME
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.
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.