Page:The wonders of optics (1869).djvu/115

Rh in the same way that these three lines are all in the same vertical plane.



Let us now examine the effects of light reflected from plane surfaces. We must first, however, notice a certain optical illusion to which we are continually falling a prey, almost without our knowledge. We always fancy objects to be in reality in the place where we see them, and, in spite of our having already enumerated a large number of these deceptions, we must still add one more to the list. In reality we rarely see objects in the place where they really are; for if by the effect of reflection, refraction, or any other cause, the rays of light are made to deviate from their course, we no longer see the object from which they proceed in its real position, but in the direction taken by the luminous pencil at the moment of entering the eye.

For instance, if the ray is bent during its passage to the eye at, and consequently reaches it in the