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

But the children still kept fast hold of his hands. "Do come with us!" Sylvie entreated with tears in her eyes.

"Well, well!" said the good-natured old man. "Perhaps I'll come after you, some day soon. But I must go back now. You see I left off at a comma, and it's so awkward not knowing how the sentence finishes! Besides, you've got to go through Dogland first, and I'm always a little nervous about dogs. But it'll be quite easy to come, as soon as I've completed my new invention----for carrying one's-self, you know. It wants just a little more working out."

"Won't that be very tiring, to carry yourself?" Sylvie enquired.

"Well, no, my child. You see, whatever fatigue one incurs by carrying, one saves by being carried! Good- bye, dears! Good-bye, Sir!" he added to my intense surprise, giving my hand an affectionate squeeze.

"Good-bye, Professor!" I replied: but my voice sounded strange and far away, and the children took not the slightest notice of our farewell. Evidently they neither saw me nor heard me, as, with their arms lovingly twined round each other, they marched boldly on.