I was lying with Billy one evening outside our hut overlooking the lake, when the solution to this puzzle came all at once into my head. The ground behind the hut sloped pretty steeply down to the lake, the length of the slope being about twenty feet, and the vertical height about six feet--that is, between the floor of our hut and the usual surface of the water. For I must observe here, lest I forget it, that the depth of water in the lake varied very much at different seasons, being far greater after a period of rainy weather than in drought, the variation being at least equal to the height of a man. And in regard to this variation a circumstance caused us much wonderment, for though when the rains were heavy the lake rose very rapidly to a certain point, we observed that it never came higher than that point, no matter how long the rains continued. When I pointed this out to Billy he saw nothing to wonder at in it, saying that the lake must be just like the sea; for though it had rained hundreds and thousands of times since the beginning of the world, the sea had never drowned the world since the Flood, and it surely would have done so unless there was some hole at the bottom that opened when the sea was getting too full. "That can't be," said I. "Well, then, how is it?" says he. "You pour water into a cup, and it'll slop over presently. The lake's a cup, though a big one; why don't it slop over after all these rains if there ain't a hole in the bottom, as I say?" "But it can't be in the bottom, Billy, or the lake would sometimes be drained quite dry," I said. "Well, it is, pretty nearly," he replied, but I would not admit that, for though the water subsided slowly after the rains had ceased, it had never sunk so low as to let us see the bottom. At low water we hunted all round the lake to see if we could find an outlet through which the water ran away, but we saw none, and remained in our puzzlement for a good while longer. However, I was beginning to tell of the notion that came into my head as we lay that evening above the lake. Being so little distant from it, I thought, why should we not sink a well in the floor of the hut, and connect it with the lake by a pipe? "What's the good?" says Billy, when I put the question to him. "For one thing, the water won't run up into the hut without a pump; at least, I've never seen water run uphill yet; and then, as soon as any savages come, you may be sure they'll spy it, and then where are you?"