“Well, I was--generally,” he said in a rather dazed fashion; and indeed it was probably the first time that he had ever found himself fully conscious of not thinking about it. Of what he was thinking about he was by no means fully conscious. “I suppose you have to be awfully clever even to understand it,” observed Margery Dale conversationally. “I don’t know,” he said, slightly stirred to the defensive. “I’m sure I could make you see--I don’t mean you aren’t clever, of course; I mean I’m quite sure you’re clever enough to see--to see anything.” “Only some sorts of things, I’m afraid,” she said, smiling. “I’m sure your theory has got nothing to do with cows and milking-stools.” “It’s got to do with anything,” he said eagerly; “with everything, in fact. It would be just as easy to prove it from stools and cows as anything else. It’s really quite simple. Reversing the usual mathematical formula, it’s possible to reach the same results in reality by treating motion as a fixed point and stability as a form of motion. You were told that the earth goes round the sun and the moon goes round the earth. Well, in my formula, we first treat it as if the sun went round the earth----” She looked up radiantly. “I always _thought_ it looked like that,” she said emphatically. “And you will, of course, see for yourself,” he continued triumphantly, “that by the same logical inversion we must suppose the earth to be going round the moon.” The radiant face showed a shadow of doubt and she said “Oh!” “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----’”