“But any of the things you mention, the milking-stool or the cow or what not, would serve the same purpose, since they are objects generally regarded as stationary.�
He looked up vaguely at the moon which was steadily brightening as vast shadows spread over the sky.
“Well, take those things you talk of,� he went on, moved by a meaningless unrest and tremor. “You see the moon rise behind the woods over there and sweep in a great curve through the sky and seem to set again beyond the hill. But it would be just as easy to preserve the same mathematical relations by regarding the moon as the centre of the circle and the curve described by some such object as the cow——�
She threw her head back and looked at him, with eyes blazing with laughter that was not in any way mockery, but a childish delight at the crowning coincidence of a fairy-tale.
“Splendid!� she cried. “So the cow really does jump over the moon!�
Green put up his hand to his hair; and after a short silence said suddenly, like a man recalling a recondite Greek quotation:
“Why, I’ve heard that somewhere. There was something else—‘The little dog laughed——’�
Then something happened, which was in the world of ideas much more dramatic than the fact that the little dog laughed. The professor of astronomy laughed. If the world of things had corresponded to the world of ideas, the leaves of the apple tree might have curled up in fear or the birds dropped out of the sky. It was rather as if the cow had laughed.
Following on that curt and uncouth noise was a silence; and then the hand he had raised to his head abruptly rent off his big blue spectacles and showed his staring blue eyes. He looked boyish and even babyish.
“I wondered whether you always wore them,� she said. “I should think they made that moon of yours look blue. Isn’t there a proverb or something about a thing happening once in a blue moon?�