s would begin
to assemble by mid-afternoon, and by four or five o'clock were all in
their lodgings.

The chimney is a capacious one, forty or fifty feet high and nearly
three feet square, yet it did not seem adequate to afford
breathing-space for so many birds. I was curious to know how they
disposed themselves inside. At the bottom was a small opening. Holding
my ear to it, I could hear a continuous chippering and humming, as if
the birds were still all in motion, like an agitated beehive. At nine
o'clock this multitudinous sound of wings and voices was still going
on, and doubtless it was kept up all night. What was the meaning of
it? Was the press of birds so great that they needed to keep their
wings moving to ventilate the shaft, as do certain of the bees in a
crowded hive? Or were these restless spirits unable to fold their
wings even in sleep? I was very curious to get a peep inside that
chimney when the swifts were in it. So one afternoon this opportunity
was afforded me by the removal of the large smoke-pipe of the old
steam-boiler. This left an opening into which I could thrust my head
and shoulders. The sound of wings and voices filled the hollow shaft.
On looking up, I saw the sides of the chimney for about half its
length paved with the restless birds; they sat so close together that
their bodies touched. Moreover, a large number of them were
constantly on the wing, showing against the sky light as if they were
leaving the chimney. But they did not leave it. They rose up a few
feet and then resumed their positions upon the sides, and it was this
movement that caused the humming sound. All the while the droppings of
the birds came down like a summer shower. At the bottom of the shaft
was a mine of guano three or four feet deep, with a dead swift here
and there upon it. Probably one or more birds out of such a multitude
died every night. I had fancied there would be many more. It was a
long time before it dawned upon me what this uninterrupted flight
within the chimney meant. Finally I saw that it was a sanitary
measure: only thus could the birds keep from soiling each other with
their droppings. Birds digest very rapidly, and had they all continued
to cling to the sides of the wall, they would have been in a sad
predicament before morning. Like other acts of cleanliness on the part
of birds, this was doubtless the prompting of instinct and not of
judgment. It was Nature looking out for her own.

In view,