2ndly—The nerves (which receive the impression) have one point of union, before they reach the brain.
Q. Why do we see ourselves in a glass?
A. The rays of light from our face strike against the surface of the glass, and (instead of being absorbed) are reflected, or sent back again to our eye.
Q. Why are the rays of light reflected by a mirror?
A. Because they cannot pass through the impenetrable metal with which the back of the glass is covered; so they rebound back, just as a marble would do if it struck against a wall.
Q. When a marble is rolled towards a wall, what is that path through which it runs called?
A. The line of the angle of incidence.
Q. When a marble rebounds back again, what is the path it then describes called?
A. The line of the angle of reflection.