the children asked their eager question. "Why should I not invoke the Muse to the help of art? A large cylindrical glass, holding a litre, stood on the table, filled with the superb water that gushes out of the slates fresh and cool, crystal clear, and chemically pure.
"Look at the water in the glass," said I; "of what color is it?"
"I don't see that it is of any color," said one. "It is red," said the other.
"But that comes from the flowers that are behind it," replied Annie. "Come round to where I am; it doesn't look red from here."
Lili ran round the table, and confessed, a little vexed, that the water was not red. She had a disposition, perhaps, like Lessing's, who was dissatisfied because the spring was always green, and not, by way of change, sometimes red.
"Is it not true, grandpa, that water has no color?"
"Yes, dear child, it is blue, but so little so that you can not see it."
"Can you see that it is blue? "
"No; but still it is blue. Look at this."
I took a little ultramarine on the end of the brush and mixed it with the water. "Does it look blue now? "
"No; I see nothing."
"Nor I. But you saw how I put a little blue color in it with the brush."
"Yes, but there was not enough of it. Put more in."
I silently took the glass and set it on a piece of white paper in the bright sunshine. "Now look from above down into it."
"It is blue!" said the little one, clapping her hands, "but only a very little."
"Look at it from the other side, where the sun is shining into it. Is it not a little bit red, like the bell-flowers which you picked yesterday? "
"That is wonderful," said the little one. "It is blue from above, a little bit red in the sun, and when we look at it from this side of the room we see nothing!"
"Think about it a little. The glass is as broad as my finger is long. But it is at least three times as high as my finger. When you look at it from the side, you see only a finger's length of water; but when you look down into it, you see through three fingers' length of water three times as much. You see it blue from the side, and three times as blue from above, don't you? "
"Is that really true?" said the little one, as she measured with her finger. She nodded that she was satisfied.
"Now imagine that the water is as deep as the height of the
