CHAPTER XII.
PURSUED.
At ten o'clock Sam harnessed up again, and shortly before noon our travellers left the waterway by which they had travelled hitherto, and passed out to the right through a cut, less than a quarter of a mile long, where a rising lock took them into the Stratford-on-Avon Canal.
Said Sam as he worked the lock, the two children standing beside and watching-- "Now see here, when you meet your clever friend Bill, you put him two questions from me.

First, why, when the boat's through, am I goin' to draw the water off an' leave the lock empty ?" Before Tilda could answer, Arthur Miles exclaimed-- "I know! It's because we 're going uphill, and at the other locks, when we were going downhill, the water emptied itself." "Right, so far as you go," nodded Sam.

"But why should a lock be left empty ?" The boy thought for a moment.
"Because you don't want the water to waste, and top gates hold it better than lower ones." "Why do the top gates hold it better ?" "Because they shut _with_ the water, and the water holds them fast; and because they are smaller than the bottom gates, and don't leak so much." "That's very cleverly noticed," said Sam.

"Now you keep your eyes alive while we work this one, an' tell me what you see." They watched the operation carefully.
"Well ?" he asked as, having passed the _Success to Commerce_ through, he went back to open the lower paddles--or slats, as he called them.
"I saw nothing," the boy confessed disappointedly, "except that you seemed to use more water than at the others." "Well, and that's just it.

But why ?" "It has something to do, of course, with going up-hill instead of down.