Page:Optics.djvu/54

 40. When an object is placed between two plane mirrors, in the first place it is reflected at each of them, which produces two images; these are again reflected at the mirrors to which they are opposite, and thus there is formed an infinite number of images growing more and more distant and more indistinct on account of the light which is lost at each reflexion.

To make this plainer, let (Fig. 36.) be an object considered as a point placed between the two mirrors,. a line through perpendicular to the two mirrors.

and so on. and so on.

An eye placed any where between the mirrors as at, will see all these images in the directions , , …, , , ….

The reader may perhaps find some difficulty in understanding how the image, for instance, can be reflected at , when it is behind the mirror , so that no light could come from to ; but he has only to remember, that the light never goes from between the mirrors; , , &c. are merely imaginary points, where the rays intersect the line.

The distances, , &c. are easily calculated. If we put for,  for , and  for  or ,