It continued raining for two or three days, greatly to our discomfort; and we made up our minds to two things: first, to have a stock of firewood ready dried; second, to build ourselves a better grate, which we could cover in with pottery ware, and thus prevent the fire from being ever extinguished. During these days we observed, as we had done before, that the lake did not rise above the high-water mark, though the rain was the heaviest since we had been on the island; and when I sought once more to account for this, and remembered the torrent pouring down the passage, it came all of a sudden into my mind that I had the true reason of it. The passage, as I have said, rose continually from the cave inwards. Well, I guessed that its upper end opened into the side of the lake, but it then rose until its highest point was pretty nearly on a level with what we called the high-water mark, and after that descended again. If it was so, it acted as a siphon, the water not flowing down the passage until the lake rose to the same height as the highest part of the passage. When I tried to explain this to Billy he said it was all gammon, because if there was an opening from the lake into the passage the water would keep on flowing through until it couldn't help but run over. He could not in the least understand that water could never rise above its own level until I showed him by means of two tanks made of pottery, one large and the other small, and then he owned that I might be right, though he said it seemed to him like saying that a ten-pound weight wouldn't send up a five-pound weight if they were put in the opposite pans of a balance. However, my discovery (supposing my reasoning was correct, and we could not prove it)--my discovery, I say, was of no practical advantage to us, indeed, rather the reverse, for it seemed to show that the tunnel from the cavern to the sea might be sometimes impassable, so that as a way of retreat from our hut it was doubly useless. When I pointed this out to Billy he said, "Never mind, master. We shall only have to fight all the harder inside, that's all," which shows how hopeful he always was. The only comfort I had was to think that our fears and anxieties might never be justified, and that Hoggett and his crew would never more visit us. CHAPTER THE SIXTEENTH OF THE ASSAULT ON THE HUT, IN WHICH BOWS AND ARROWS PROVE SUPERIOR TO MUSKETS