Because the water runs to the bottom of the bubble until its top becomes so thin as to burst.
Can we tell the color of any object by touching it?
No; we must see it in order to tell its color.
How do we know this?
If there are two coats, one blue and the other black, we cannot tell which is the blue one or which is the black one, by feeling them.
What is necessary in order to see the colors?
Light is necessary; because all colors come from the rays of light.
Can we see the different colors in the ray itself?
We cannot; because God has so blended them together that they cannot be seen by us.
When most of the rays of light pass through a substance, what is said of it?