A Frenchman named Denys Papin had built the first steam-engine with a piston. He had seen certain experiments that showed him how much strength there was in compressed air. He had noticed that air pressure could lift several men off their feet. His problem therefore was how best to compress the air, or, as it appeared to him, how to secure a vacuum. His experiments proved that he could do this by the use of steam. He took a simple cylinder and fitted a piston into it. Water was put in the cylinder under the piston, a fire was lighted beneath it, and as the water came to the boiling point the piston was forced upward by the steam. Then the fire was taken away, and as the steam in the cylinder condensed, the piston was forced down by the air pressure above. He fastened the upper end of the piston to a rope, which passed over two pulleys. If a weight were hung to the other end of the rope it would be raised as the piston was forced down. In that way the air pressure did the work of lifting the weight, and the necessary vacuum was obtained by forming steam and then condensing it in the cylinder. This was a very primitive device, requiring several minutes for the engine to make one stroke, but it was the beginning of the practical use of steam as a motive power. Thomas Newcomen, an English blacksmith by trade, first put Papin’s idea to use. Instead of the rope and pulleys Newcomen fastened a walking-beam to the end of the piston, and attached a pump-rod to the other end of the walking-beam. He used the steam in the cylinder only to balance the pressure of the air on the piston, and let the pump-rod descend by its own weight. As the steam condensed the piston fell, and the pump-rod rose again. By this means he could pump water from a mine, or lift coal. His first engine was able to lift fifty gallons of water fifty yards at each stroke, and could make twelve strokes a minute. At first he condensed his steam by throwing cold water on the outside of the cylinder, but one day he discovered that the engine suddenly increased its speed, and he found that a hole had been worn in the cylinder, and that the water with which he had covered the top of the piston was entering through this hole. This condensed the steam more rapidly, and he adopted it as an improvement in his next engine. A little later a boy named Humphrey Potter, who had charge of turning the cocks that let the water and steam into the cylinder, found a way of tying strings to the cocks so that the engine would turn them itself, and so originated what came to be known as valve-gear.