Robert Louis Stevenson

As from the house your mother sees
You playing round the garden trees,
So you may see, if you will look
Through the windows of this book,
Another child, far, far away,
And in another garden, play.
But do not think you can at all,
By knocking on the window, call
That child to hear you.  He intent
Is all on his play-business bent.
He does not hear, he will not look,
Nor yet be lured out of this book.
For, long ago, the truth to say,
He has grown up and gone away,
And it is but a child of air
That lingers in the garden there.