Nearly as high as the water in the basin.
What is the water flowing from such an opening called?
It is called a fountain.
What makes the water shoot up in a fountain?
The pressure of the water in the basin forces it to shoot up in the fountain.
To what does water always tend?
Water always tends to fall to a level.
What instrument is constructed on this principle?
The water-level.
What is a water-level?