Through the later centuries, up to the 17th, hut little progress was made either in the ac quirement of a knowledge of the properties of steam or in its application to useful purposes. Some forms of "xolipile,') furnished a steam jet for improving the draft of the chimney, apparatus for turning the spit and even more ambitious uses were either attempted or sug gested; hut, until Da Porta's treatise on pneu matics appeared in 1601, in which a steam-foun tain was described, and the description in 1629 of an impulse steam-turbine, by Branca, no de velopment took place of any real importance.
the engine. The study of the steam-engine thus comprehends the ideal, the purely ther modynamic, case and the real case with its various wastes, thermodynamic and extra-ther modynamic, as well as an investigation of the principles and practice in the design and con struction of the real engine.
Engines.— The power of steam and the em ployment of that fluid in various sorts of en gines have been familiar to mankind from an unknown and possibly prehistoric period. The earliest known record is that of Hero, who, in his (Pneumatica) of which the manuscript was produced at Alexandria, about 120 B.c., de It was not until the second Marquis of Wor cester, Edward Somerset, constructed a steam fountain (1650) and employed it in raising water from the moat to the top of the tower of Raglan Castle, and later erected another for similar purposes at Vauxhall, that the story of the evolution of the steam-engine really begins. Meantime the scientific men of the later cen turies were acquiring some exact knowledge of the nature of steam, earlier confounded with other gases, and some familiarity with its latent powers.
Steam power first became an acknowledged industrial agent and useful as a prime mover when Savery, at the' beginning of the 18th century (1698), made Worcester's steam-foun tain practically applicable to the drainage of mines and the elevation of water for water supply generally. This apparatus, which could not be properly called an engine, consisted of a pair of cylindrical or ellipsoidal forcing yes sets" which were alternately filled with water, by the production of a vacuum within the vessel, and emptied by the introduction of high pressure steam from an adjacent boiler; the one being emptied while the other was filling and vice-versa, This apparatus, introduced by Sav ory, improved and further made known by Desaguliers and by Smeaton, was known and in use before the year 1773 throughout the world where mining at considerable depths and in presence of water was carried on. The steam
fountain is still in use and is known as the upulsometer." Newcomen's steam-engine, the first steam engine properly so termed, the first which con sisted of a train of mechanism as distinguished from the Hero steam-fountain, which was a piece of apparatus without moving parts, was patented in 1705. It consisted of a steam-cylin der and piston, actuating a beam, above from the opposite end of which was pendant the pump-rod operating the pumps in the shaft of the mine; it was always used as a steam pump ing engine. Thomas Newcomen and his part ner, John Calley, are thus to be credited with the invention and introduction of the modern steam-engine with all its essential elements as a pumping engine. It was the improvement of this engine by the addition of various valuable devices which gave James Watt his fame and fortune.
This earliest type was a condensing en gine in which condensation was effected by means of a jet of water directed into the steam cylinder when the pressure on the under side of the piston was to be removed. The upper side was open to the air, there being no upper cylinder-head. The engine was thus operated by the atmospheric pressure, steam being held at about atmospheric pressure and only em ployed to secure a vacuum below the piston. The pressure of the atmosphere depressing the piston, the pump-rod on the opposite end of the beam was raised and the Dump filled. With the fall of the pump-rod the water was forced out of the pump and rdised to the upper level. The weight on the outer end of the beam always overbalanced the weight of the piston and attachments sufficiently to do the required work. This type of engine remained in use for a century, and old engines of New comen's time are still in existence. The type became known, later, as the Cornish engine, Watt's improvements having been meantime added. After Newcomen's death, the machine was improved in details by Desaguliers and by Smeaton, who considerably increased its econ omy by attaching wood to the piston and cylinder-head to prevent what has been called ((cylinder condensation" by action of alter nately heated and cooled metal in contact with the steam. This was probably the first rec ognition in construction of this important phe nomenon.