These were two problems which had to be solved at once. For the time being, horses could still be used to haul the coal-wagons, but the pumping question demanded the application of special machinery. Several inventors were busy trying to solve the difficulty. They all knew that steam would have to be used in their new engine. The idea of the steam engine was very old. Hero of Alexandria, who lived in the first century before Christ, has described to us several bits of machinery which were driven by steam. The people of the Renaissance had played with the notion of steam-driven war chariots. The Marquis of Worcester, a contemporary of Newton, in his book of inventions, tells of a steam engine. A little later, in the year 1698, Thomas Savery of London applied for a patent for a pumping engine. At the same time, a Hollander, Christian Huygens, was trying to perfect an engine in which gun-powder was used to cause regular explosions in much the same way as we use gasoline in our motors.