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 . . . And--and I've got the reason somewhere inside my head, but I
can't catch hold of it."

"I'll put it another way. This boat's mod'rate well laden, an' she
takes more water lockin' up than if she was empty; but if she was empty,
she'd take more water lockin' down. That's a fac'; an' if you can give
me a reason for it you'll be doin' me a kindness. For I never could
find one, an' I've lain awake at nights puzzlin' it over."

"I bet Bill would know," said Tilda.

Sam eyed her.

"I'd give somethin'" he said, "to be sure this Bill, as you make such a
gawd of, is a real person--or whether, bein' born different to the rest
of yer sex, you've 'ad to invent 'im."

Many locks encumber the descending levels of the Stratford-on-Avon
Canal, and they kept Sam busy. In the intervals the boat glided deeper
and deeper into a green pastoral country, parcelled out with hedgerows
and lines of elms, behind which here and there lay a village half
hidden--a grey tower and a few red-tiled roofs visible between the
trees. Cattle dotted the near pastures, till away beh