Portuguese Voyages and Possessions
The first great navigational feat that followed the invention of the compass was that performed by the Portuguese, Bartholomew Dias, who conceived the idea of reaching India by going around Africa, and sailed down the west coast of Africa as far as its southern end, later called the Cape of Good Hope. It was a tremendous undertaking, and it had tremendous results; for it demonstrated the possibilities of great ocean voyages, proved that the road to India was very long, and led to the expedition of Columbus, six years later. It was also a great invention, both in brilliancy of conception and excellence of execution, although Dias did not reach India. The second great navigational feat was performed by Christopher Columbus in 1492. Before that time it was conceded by most men of learning and reflection that the earth was spherical; and it was realized that, if it was spherical, it might be possible by sailing to the westward to reach India, the goal of all commercial expeditions in that day. Columbus is not to be credited with the first conception of that possibility.
Hero's Engines
One of the early influences of the art of printing was to bring to the notice of some restless minds the writings of Hero and Archimedes. In Hero's Pneumatics, published more than 120 years before Christ, he gives such a clear account of an invention of his own, in which the expansive force of steam was used to give and maintain motion, as to establish thoroughly his right to the basic invention of the steam engine. He described three apparatus that he devised. In one, the currents of air and aqueous vapor rising through a tube from a hollow sphere, containing water, under which a fire is burning, support a ball placed immediately above the tube, and make it seem to dance. In another apparatus, a hollow sphere into which steam has arisen from what we now call a boiler, is supported on a horizontal or vertical axis, and provided with tubes that protrude from the sphere, and are bent at right angles to the radius and also to the pivot. The inner ends of these tubes lie within the sphere, so that the steam passes from the sphere through the tubes. As soon as this happens, the sphere takes up a rapid rotation, that continue so long as the steam continues to escape from the nozzles of the tubes, which point rearwardly. A third apparatus was merely an elaboration of the second, in that the sphere was connected with an altar which supported a large drum on which were figures representing human beings. The fire being lighted, the sphere would soon begin to revolve, and with it the drum; and the figures on it would seem to dance around, above the altar. The invention was probably to impress the people with the idea that the priests were exerting supernatural power.
Hero's Altar Engine
A third apparatus [from Hero] was merely an elaboration of the second, in that the sphere was connected with an altar which supported a large drum on which were figures representing human beings. The fire being lighted, the sphere would soon begin to revolve, and with it the drum; and the figures on it would seem to dance around, above the altar. The invention was probably to impress the people with the idea that the priests were exerting supernatural power.
Leupold's Engine
In 1725, Jacob Leupold invented an engine, in which the work was done by steam alone, instead of by the atmosphere, as in the engines that immediately preceded it. Leupold used two cylinders. They were open at the top to the atmosphere as in the others, but154 he used higher pressures of steam, and arranged a four-way cock between the bottoms of the two cylinders in such a way that the bottom of each cylinder, in its turn, was connected to the boiler or to the open air. Each cylinder actuated directly a separate vibrating beam, which in turn actuated the piston of a pump; the two pistons acting reciprocally, each drawing up water in its turn. In 1765, James Watt made the very great improvement of providing a condenser separate from the cylinder of the engine, so that the great loss of heat caused by cooling the cylinder and then heating it at each stroke was wholly avoided. He covered the cylinder entirely, and surrounded it with an external cylinder kept always full of steam, that maintained the cylinder at a high temperature. The steam, instead of being condensed within the cylinder, after it had done its work, was allowed to escape into the condenser. To facilitate this action, the condenser was fitted with an air-pump that maintained a good vacuum in it. In 1769, Watt invented an improvement that consisted mainly of means whereby the supply of steam to the cylinder could be shut off at any desired part of the stroke, and the steam allowed to complete the rest of the stroke by virtue of its expansive force. This invention increased tremendously the efficiency of the engine: that is, the amount of work done with a given amount of steam.