Jonathan Hulls patented in England in 1736 a marine steam engine, and in 1737 published a description of a Newcomen engine applied to his system for towing ships. William Henry, of Pennsylvania, tried a model steamboat on the Conestoga river in 1763. This was practically the state of the art, in 1763, when James Watt entered the field. His brilliant inventions harnessed steam to more than pumping engines, made it a universal servant in manifold industries, and started it on a career which has revolutionized the trade and manufactures of the world. To understand what the nineteenth century has done in steam motive power we must first know what Watt did in the eighteenth century, as he then laid the foundation on which the later inventions have all been built. Taking up the crude but successful working engine of Newcomen, a model of which had been sent to him for repairs, he began an exhaustive study of the properties of steam and of the means for producing and controlling it. He found it necessary to devise a new system. Watt saw that the alternate heating and cooling of the cylinder made the engine work slowly and caused an excessive consumption of steam. He concluded that “the cylinder should always be as hot as the steam that entered it.” He therefore closed the cylinder and provided a separate condensing vessel into which the steam was led after it raised the piston. He provided an air-tight jacket for the cylinder, to maintain its heat. He added a tight packing in the cylinder-head for the piston-rod to move through, and a steam-tight stuffing-box on the top of the cylinder. He caused the steam to alternately enter below and above the piston and be alternately condensed to drive the piston down as well as up, and this made the engine double-acting, increasing its power and speed. He converted the reciprocating motion of the piston into a rotary motion by the adoption of the crank, and introduced the well-known parallel motion, and many other improvements. In short, he demonstrated for the first time by a practical and efficient engine that the expansive force of steam could be used to drive all ordinary machinery. He then secured his inventions by patents against piracy, and sustained them successfully in many a hard-fought battle. It had taken him the last quarter of the 18th century to do all these things. Watt was the proper precursor of the nineteenth century inventions, as in him were combined the power and attainments of a great scientist and the genius of a great mechanic. The last eighteen years of his life were passed in the 19th century, and he was thus enabled to see his inventions brought within its threshold and applied to those arts which have made this age so glorious in mechanical achievements.