How else can it be shown that water will rise to the same level in different vessels?
By a reference to [Fig. 21], this may be seen.
Fig. 21.
Let these vessels be made so as to connect with each other by the tube at the bottom; then, when water is poured into one of them, it will rise up in each of the others, so as to be the same height in all.
Where is this principle used to benefit mankind?
It is used in supplying the inhabitants of cities with water.
What must be built in order to supply a city with water?
A reservoir must be built.
What is a reservoir?