degrees." He looked apologetic.

"Tell me everything; I have been waiting a long time."

David reflected a few moments and then began:--

"The first of my books as I have arranged them, considers what we
call the physical universe as a whole--our heavens--the stars--and
discusses the little that man knows about it. I used to think the
earth was the centre of this universe, the most important world in
it, on account of Man. That is what the ancient Hebrews thought. In
this room float millions of dust-particles too small to be seen by
us. To say that the universe is made for the sake of the earth
would be something like saying that the earth was created for the
sake of one of these particles of its own dust."

He paused to see how she received this.

"That ought to be a great book," she said approvingly. "I should
like to study it."

"The second takes up that small part of the universe which we call
our solar system and sums up the little we have learned regarding
it. I used to think the earth the most important part of the solar
system, on account of Man. So the earliest natural philosophers
believed. That is like believing that the American continent was
created for the sake, say, of my father's farm."

He awaited her comment.