The little brook was a safe stream for the boy and the girl to play
beside. Nor did they know, then, that their streamlet flowed on and on
until it joined the river; and that the river, in its course, led it
past great cities that poured into it the poisons and the filth of
their sewers, fouling its bright waters, until it was unfit for
children to play beside.

They did not know, _then_--but the woman knew, _now_.

And what--she thought as she came back from her Yesterdays--what of
the boy who had played with her beside the brook? He, too, must have
learned what happened to their brook. In learning, what had happened
to him--she wondered--and wondering, she was afraid.

Because she was no longer ignorant, she was afraid for the mate of her
Yesterdays. Not that she thought over to meet him again. She did not
wish, now, to meet him for she was afraid. She would rather have him
as he was in her Yesterdays.

Slowly the woman turned away from the quiet seat beside the brook. It
was time for her to go.

Not far away, she passed the gray haired policeman, who again smiled
and touched his hat.

Smiling in return she bade him: "Good afternoon."

"Good afternoon, Miss," he said, still smiling gravely. "Come again,
Miss, when ye's want a breath of air that's pure and clean."