Experiment 39. To start a siphon.
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.