together when the door was opened. This, however, did not seem a very likely event, though the Gardener patiently tried all the small keys, over and over again.
At last the Professor ventured on a gentle suggestion. "Why not try the large one? I have often observed that a door unlocks much more nicely with its own key."
The very first trial of the large key proved a success: the Gardener opened the door, and held out his hand for the money.
The Professor shook his head. "You are acting by Rule," he explained, "in opening the door for me. And now it's open, we are going out by Rule——the Rule of Three."
The Gardener looked puzzled, and let us go out; but, as he locked the door behind us, we heard him singing thoughtfully to himself
"He thought he saw a Garden-Door
That opened with a key:
He looked again, and found it was
A Double Rule of Three:
'And all its mystery,' he said,
'Is clear as day to me!'"
