“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.