“Perfectly fair.  Suppose that Mrs. Benoit stood behind your curtain there, and that you had never seen her; how could you know that she has a dark skin?”

“Why I could not.”

“Yes, you could—­if there were rents in the curtain.”

“But what are you talking of, sir?”

“Only telling you, in answer to your question, how I know the sun to be a dark body.”

“But there is no curtain over the sun.”

“That proves you are no philosopher, Daisy.  If you were a philosopher, you would not be so certain of anything.  There is a curtain over the sun; and there are rents or holes in the curtain sometimes,—­so large that we can see the dark body of the sun through them.”

“What is the curtain?  Is that the light?”

“Now you are coming pretty near it, Daisy,” said the doctor.  “The curtain, as I call it, is not light, but it is what the light comes from.”

“Then what is it, Dr. Sandford?”

“That has puzzled people wiser than you and I, Daisy.  However, I think I may venture to say, that it is something like an ocean of flame, surrounding the dark body of the sun.”

“And there are holes in it?”

“Sometimes.”

“But they must be very large holes to be seen from this distance?”

“Very,” said the doctor.  “A great many times bigger than our whole earth.”

“Then how do you know but they are dark islands in the ocean?”

“For several reasons,” said the doctor looking gravely funny; “one of which reasons is, that we can see the deep ragged edges of the holes, and that these edges join together again.”

“But there could not be holes in our ocean?” said Daisy.

Dr. Sandford gave a good long grave look at her, set aside his empty plate which had held raspberries, and took a chair.  He talked to her now with serious quiet earnest, as if she had been a much older person.

“Our ocean, Daisy, you will remember, is an ocean of fluid matter.  The ocean of flame which surrounds the sun is gaseous matter—­or a sort of ocean of air, in a state of incandescence.  This does not touch the sun, but floats round it, upon or above another atmosphere of another kind—­like the way in which our clouds float in the air over our heads.  You know how breaks come and go in the clouds; so you can imagine that this luminous covering of the sun parts in places, and shews the sun through, and then closes up again.”

“Is that the way it is?” said Daisy.

“Even so.”

“Dr. Sandford, you said a word just now I did not understand.”

“Only one?” said the doctor.

“I think there was only one I did not know in the least.”

“Can you direct me to it?”

“You said something about an ocean of air in a state—­what state?”

“Incandescence?”

“That was it.”

“That is a state where it gives out white heat.”