They soon tested their instrument by experiment. Taking some sand, Sammy strewed it over the wheel, and put a lump of clay on it while Archie turned. He did this in order that he might be able to get the vessel off, as he knew the clay would stick to the wood; but when he put his hands on the clay the wheel turned round under it, and the clay tumbled to the floor. Finding that would never do, he swept off all the sand, and flung the lump down hard on the wood, where it stuck fast (as Uncle Seth had told him he saw the potters do), put his hands on each side of the clay, and brought it up to a sugar-loaf form, and then pressed it down to break the air-bubbles, then put his thumbs into the middle of the lump, and his fingers outside. The clay instantly assumed a circular form, and became hollow. "Oh, oh! It's doing it!" shouted Sam. "Doing what?" cried Archie, who on his knees could not see what was going on. "It's growing hollow. It's making a pot. Oh, it's growing thinner and thinner!" Indeed it was; for Sammy not only stuck his thumbs into the lump, but kept separating his hands, till, the walls of the pot growing thinner and thinner, both thumbs broke through, and there were only two long, wide ribbons of clay, and no bottom; for he had pressed his hands down so hard as to scrape through to the wood. He uttered a yell of dismay, and Archie ran to look. "Only see there," said Sam, taking up part of the side: "see how smooth it is! I couldn't have made it so smooth the way I did before. Oh, if it hadn't bursted!" "What made it do so?" "Don't know: guess I can do better next time." Next time he succeeded in making something hollow, but it was almost as big at the top as at the bottom; the sides were thick in one place, and thin in another: but the boys thought it was nice till they tried to take it from the wheel, when they found Sammy had poked his fingers through the bottom to the wood. Archie was now to try his hand: the wheel had made but a few revolutions when he shouted,-- "Stop!" He had pressed his hands so close together, that at the top there was a cone of clay, and a round lump on the wheel, without the sign of a hollow. The next time he made something hollow; but the sides were so thin they would not stand, but tumbled down in a heap as soon as he took his hands off. Now it was Sammy's turn again. While turning the wheel for Archie, he had been reflecting upon the causes of his poor success; and this time made a pot that was all right at the bottom, and of a proper thickness, only rather bulging in the middle. They were greatly delighted, but, in trying to take it from the wheel, tore it in pieces. Sammy made another attempt, and met with still better success. They dared not take this pot from the wheel, yet were unwilling to ask Uncle Seth, or let him know any thing about their proceedings till they had made more progress.