“This time I am looking at the cows themselves!  Those over there are beautiful creatures, and there is a clear spring of water in the corner of the pasture.  When we come to the farmhouse where they belong, we will stop to buy some milk, and Miss Dodo shall have supper; for even Mammy’s buns, when they have been travelling about all day in a basket, would, be rather dry without milk.”

“But wouldn’t the milk be good if the cows were not pretty, and there was no spring in the pasture?” asked Nat, who must have a reason for everything.

“It is not a question of pretty cows; it is whether they are clean and healthy or not, that makes the milk good or bad.  And good pure water to drink, from a spring that is not near any barnyard or outbuilding, is one of the best things for keeping cows in good health.”

Meanwhile they had driven up to a farmhouse, almost as large as their own, and the mistress, who was arranging her pans for the evening milking, said they might have cold milk then, or fresh warm milk if they would wait a little while until the cows came home.

Under the back porch was a cage with a little Owl in it, and the woman said it belonged to her boy.  Joe, for that was his name, was about Rap’s age, and soon made friends with them.  They told him where they had been spending the day, and about their uncle’s wonder room, and the birds at Orchard Farm.  “Have you got a Hummingbird’s nest on your farm, and a Swallow chimney?” Joe asked anxiously.

“No, not exactly,” said Nat, hesitating.  “There are some birds in Uncle Roy’s chimney, but we haven’t found a Hummingbird’s nest yet, though there are lots of the birds about the garden.”

“Well, there’s a Hummingbird’s nest in our crab-apple tree, and we own the biggest Swallow chimney there is in the county!  Pa says so, and he knows,” said Joe proudly.  “If you’ll come with me and not grab the nest, I’ll show it to you.  It’s a widow Hummingbird, too.  I’ve never seen her mate since she began to set, but before that he was always flyin’ round the honeysuckles and laylocks, so I’m sure he is dead.”

“May I come too?” asked the Doctor.

“Pleased to have you, sir,” said Joe, making a stiff little bow.  “I’d have asked you, only most men folks don’t set much store by birds ’nless they are the kind they go gunnin’ for.  Only pa does.  He likes any kind o’ bird, whether it sings or not, and he’s powerful fond of the Swallows in our chimney.  He says they eat the flies and things that tease the cows down in the pasture, and since those Swallows came to our chimney we haven’t had to put fly-sheets on the oxen when they are in the pasture—­not once.”

“Now, children, you see what good the Sky Sweepers do,” said the Doctor.

“Sky Sweepers!  We don’t call ’em that!  We call ’em Chimney Swallows!”

Then the children told Joe about the Bird Brotherhoods.

“Stand on this box,” said Joe to Dodo, “and look hard at that small slantways branch, with the little bunch on it!”