The eye also has to be changed a little when we look from near to distant objects.

Look out of the window at a tree a long way off.

Now place a lead pencil between the eyes and the tree.

You can scarcely see the pencil while you look sharply at the tree, and if you look at the pencil you cannot see the tree distinctly.
~22.~ There is a little muscle in the eye which makes the change needed to enable us to see objects close by as well as those which are farther away.

When people grow old the little muscles cannot do this so well, and hence old people have to put on glasses to see objects near by, as in reading.