"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."