Another invention also utilizing external power, made near the end of the eighteenth century, was the hydrostatic press. It consisted of a vertical cylinder, fitted with a piston prevented by suitable means from rising, except against great pressures; the piston resting on a liquid in the bottom of the cylinder, which was connected by a small pipe with a small pump, by which more liquid could be forced in. When the pump was operated the pressure per square inch on the piston of the pump was communicated to each square inch of the large piston in the press, and a force exerted equal to that pressure multiplied by the difference in area of the two pistons. This is the model on which hydraulic jacks and many other hydraulic mechanisms are constructed; and it has taken a prominent part in the development of the science of hydraulics ever since it was invented. Because of the gradual recognition of the value of sea-commerce in the British Isles, and the fact that the stormy seas adjacent necessitated the construction of ships at once sturdy and yet capable of speed, much study and experimentation were carried on during the eighteenth century, especially in England. In these experiments, the invention by Archimedes of the hydrostatic principle of buoyancy supplied the starting-point, and gave an excellent illustration of the influence of invention on history: for from experiments and investigations on floating bodies carried on in England, based on the invention of Archimedes, and followed by others of English origin, sprang England's merchant marine and England's navy and England's domination over a quarter of the land on the surface of the earth. The eighteenth century closed with the invention of two very important mechanisms that reinforced the power of the human hand with power drawn from external sources: these were the threshing machine and the cotton gin; the former invented by Andrew Meikle in 1788, and the latter by Eli Whitney in 1793. It would be hard to decide with knowledge as to which has had the greater influence in constructing the machine of civilization; but it is not at all hard to realize that the machine of civilization could not have attained its present stage without the assistance of both. One of the last important inventions of the century was that of an art entirely new, as distinguished from inventions like the cotton gin, that merely increased the value of an art already in existence. This was the invention of lithography, or printing from stone, made by Alois Senefelder in 1796. The first thing printed by him was a piece of music. While this invention was more brilliant than those of Meikle and Whitney, it was hardly so important. Nevertheless, it was important in a high degree and made a valuable addition to civilization.