Seeing.
Of all the senses, that of seeing is the most noble, commanding and useful. It enables us to perceive thousands of objects at a glance, with their forms, colors, and distance.
The mechanical structure of the eye is very curious, but I shall not describe it now. It is sufficient to say that light is the great instrument by which vision is performed. This is supposed to consist of innumerable particles, inconceivably small, which proceed in straight lines from every part of luminous or shining bodies. These fly with a velocity ten million times as swift as a cannon ball, for they come from the sun to the earth in eight minutes!
These rays of light enter the ball of the eye at the pupil; and at the bottom of a cavity in the ball, called the retina, a little picture is painted of every object placed before the eye. It is this little picture that enables us to see; and we see distinctly, or otherwise, as this is clear or obscure. A very curious thing is, that this picture paints everything reversed, that is, upside down. The reason why we do not, therefore, see things upside down, is a matter that has puzzled greater philosophers than Bob Merry.