balances behind like a rudder and the head sticks out in front like the bowsprit."
"You are right, my boy," said the Doctor, looking at him attentively; "and would you also like to know how this beautiful boat is made? If a ship-builder could plan a vessel that would go through wind and water as birds do, he would be the wisest man in the world. But you see, Rap, a man did not plan any bird.
"I will go down and ask your mother to let you come and hear the stories with the other children—how would you like that, Rap?"
"Will you? Will you really let me come? Oh, I am so glad! I know mother'll let me any day but Monday and Thursday, because I have to watch clothes on those days."
"Wash clothes?" said Dodo in surprise.
"No, watch them," replied Rap, laughing. "Those two days the miller lets mother spread her things to whiten in his big meadow, and I have to watch and see that they are not stolen or don't blow away."
"Isn't it very stupid to sit there so long?"
"Oh, no, it's lovely; for there are lots of birds and things about."
"To-morrow will be Wednesday," said the Doctor. "Come up to Orchard Farm by nine o'clock, Rap, and we will begin our lessons with this little White-throated Sparrow Nat has found."
"And uncle!" cried Dodo, "you must make inch measures on our middle fingers with violet ink, the way you did to Olive's when she was little."
CHAPTER IV
THE BUILDING OF A BIRD
It rained on Wednesday—a warm spring rain, swelling the rivers and ponds, and watering the newly planted garden; but discouraging the birds in their nest-building, and disappointing Nat and Dodo, who wished to have their lesson in the orchard.
"Come in here, children," said the Doctor. "The wonder room, as Dodo calls it, is a good place for a talk about feathers and bones, and the rest of the things birds are built of. I have sent for Rap, too, so that the trio may be complete."
"Feathers and bones for building birds?" said Nat. "What a queer idea for a bird story."
"Not a bird story exactly," answered the Doctor. "But some things are true of all birds, and you must know them if you wish to understand the reason why of any bird in particular."
In a few minutes the three children were seated on the wide settle, with a cheery log fire, to make them forget the outside dampness. Quick, the fidgety little fox-terrier, sat by the hearth, watching a possible mouse hole; and Mr. Wolf, the tawny St. Bernard, chose the rug as a comfortable place for finishing his morning toilet.
Olive presently joined the group. The Doctor took the dead White-throated Sparrow from the table, and began to walk about the room, stopping now in front of the fire and then by the window.
"Here is a Sparrow, different from every other kind of Sparrow, different indeed from any other sort of bird in the world—else it would not be the particular sort of a Sparrow called the White-throated. But there are a good many things that it has in common with all other birds. Can you tell me some of them?"
"I know!" said Dodo; "it has a good many feathers on it, and I guess all kinds of birds wear feathers, except some when they are very little in the nest."
"Quite right, little girl," said the Doctor. "Every bird has feathers, and no other animal has feathers. So we say, 'A bird is known by its feathers.' But what do you suppose its feathers are for?"
"To make it look nice and pretty," said Dodo promptly.
"To make it lighter, so's it can fly," added Nat.
"To keep it warm, too, I guess," was Rap's answer.
"Well, you are all three partly, but not quite, right. Certainly the beauty of a bird depends most on its feathers, being not even skin-deep, as you may well believe, if you ever noticed a chicken Mammy Bun had plucked. But, Nat, how can feathers make a bird lighter, when every one of them weighs something, and a bird has to carry them all? They make a bird a little heavier than it would be without them. Yet it is quite true that no bird could fly if you clipped its wings. So some of its feathers enable it to fly—the large ones, that grow on the wings. Then, too, the large ones that make the tail help the bird to fly, by acting like a rudder to steer with. Perhaps the small ones too, all over the body, are of some help in flight, because they make a bird smooth, so that it can cut through the air more easily—you know they all lie one way, pointing backward from their roots to their tips. Then when Rap said feathers keep a bird warm, he guessed right. Birds wear plumage as you do clothes, and for the same purpose—to look nice and keep warm."
"But what is 'plumage,' Uncle Roy?" asked Dodo; "I thought you were talking about feathers."
"So I was, missy. Feathers are the plumage, when you take them all together. But see here," added the Doctor, as he spread the Sparrow's wings out, and held them where the children could look closely; "are the wings all plumage, or is there something else?"
"Of course there's something else to wings," said Dodo; "meat and bones, because I've eaten chickens' wings."
"Why didn't you say, Dodo, because there has to be something for the feathers to stick into?" said Nat decidedly.
"You both have very good reasons," said the Doctor. "The plumage of the wings grows out from the skin, just as feathers grow from any other part of the body, only the large ones are fastened to the bones, so that they stay tight in their proper places. If they were loose, they would fly up when the bird beats the air with its wings, and get out of order. See how smoothly they lie one over another! When the bird closes its wings, they come together snugly along its sides. But when the wing is spread, they slide apart—yet not too far to form a broad, flat surface, quite stiff, but light and elastic. By beating the air with the wings birds fly along. It is something like rowing a boat. This surface pushes against the air as the flat blade of an oar pushes against the water. That is why these large stiff feathers are called the rowers. When the Wise Men talk Latin among themselves, they say remiges, for 'remiges' means rowers."
"But, Doctor," said Rap, who was looking sharply at the Sparrow's wing, "all the feathers are not like that. Here are a lot of little ones, in rows on top of the wing in front, and more like them underneath, covering over the roots of the rowing feathers. Have they any name?"
"Oh, yes! Everything you can see about a bird has its own name. Those small feathers are called coverts, because they cover over the roots of the rowers. Those on top are the upper coverts; those underneath are the under coverts, or lining of the wings. Now notice those two pretty bands of color across the Sparrow's wing. You see one band is formed by the tips of the longest coverts, and the other band by the tips of the next longest coverts. Those two rows of feathers are the greater and middle coverts, and all the smallest feathers, next to the front edge of the wing, are called lesser coverts. Now look at the tail, Rap, and tell me what you can find."
"Why, there is a bunch of long stiff feathers like rowers, that slide over each other when you spread the tail, and a lot of short feathers that hide the roots of the long ones. Are they rowers and coverts too?" "A bird does not row with his tail—he steers with it, as if it were a rudder; and the long feathers are therefore called rudder-feathers—or
