o, half to
herself.

"I don't exactly know," said Rap; "but I think it is because the earth
goes round every day, making the water tip from one side to the other
and then back again."

"Then why doesn't it all tip off into the sky?" persisted Dodo.

"I guess--because--that is, I don't know," stammered Rap. "I must ask
Uncle Roy to tell us, and why the earth down here on the shore stays
sharp and gritty when it is wet; for when the earth up at the Farm is
wet, it makes sticky mud," said Dodo.

"Yes," said Nat, "and why the stars are of such different sizes, and
seem to stay quite still, except some that go along like that big bright
one over there."

"Quok! Quok!" cried a strange voice from the marshes back of the beach.
"Quok, quok, quok, quok!" answered other voices.

"What can that be?" said Nat; "it isn't a Whip-poor-will, or a
Nighthawk--it must be one of the cannibal birds. Uncle Roy, what kind of
birds are those calling away over in the marshes?" But the Doctor was
not within hearing, and it was some time before they found him, sitting
by the cabin door smoking his pet outdoor pipe, which was made of a
corn-cob.

"Did you hear the Night Herons calling as you came up?" he asked.

"We heard a very queer squawky sound, and came to ask you what it was,
for we couldn't guess," said Nat. "What is a Night Heron--a cousin of
the Nighthawk, who lives near the water?"

"I don't think it's a water bird," said Rap, "because I have heard that
same squawking up by the mill."

"But is not the mill close to the pond?" said the Doctor, smiling.

"Why, yes, to be sure--but I was thinking of salt water."

"That is a distinction that applies to few of our water birds; when we
speak of the birds that wade, paddle, swim, and dive, we must remember
that they may do so in lakes, rivers, bays, or the ocean, according to
their individual habits. In fact, some members of a single family prefer
fresh water, while their brothers are more fond of the salt sea. This is
the case in the family of the Night Heron."

"Where does he belong?" asked Rap, "with the paddling birds or the
swimming ones?"

"With the paddlers and waders."

"See, here comes the moon up out of the water and it makes a shiny path
up to our feet and Olaf is rowing back right down it and the stars have
stopped winking and are getting dim," said eager little Dodo, with an
"and" wherever she ought to have stopped to breathe, as usual. "Hark!
the Herons are squ