Passing over all these therefore as foreign to our subject, the first engine which it is necessary to describe is that of Newcomen (1705) ; it constitutes the connecting link between the steam-pumps alluded to, and the modern engine, of which it contained the germ, and into which it was converted by the genius of Watt. [WATT, JAMES, iu NOG, Div.) In the subjoined diagram, A represents a cylinder open at the uppo Compared with water at its greatest degree of condensation, the density of steam at 212° Fahr. is exactly 1695 less than that of the water, or nearly 1700, as was before stated; or in fact, one volume of water yields nearly 1700 volumes of steam. This is worthy of remark; for the volumes of the oxygen and hydrogen, contained in a given volume of water, occupy under atmospheric pressure a space equal to 2500 times the volume of the latter. It has been suggested that the condensation which thus appears to have taken place during the com bination of the permanent gases referred to, may be explained by some change in their electrical state; and it is well known that the evolution of steam, under high pressures, does give rise to electrical phenomena of a very remarkable but hitherto only partially studied description. 31essrs. Armstrong, Faraday, Schafthoentl, and Becquerel have, indeed observed that when steam, changed with water in suspension, escapes in such a manner as to exercise friction against a substance opposed to its passage, a development of electricity takes place, and that generally the water or the vapour is positive, and the opposing substances negative. The form, the nature, and the temperature of the orifices affect the development of the electricity to a great extent, and especially does heat retard it; at the same time the amount of elec trical action depends on the purity of the water, for a small quantity of salt or acid destroys the property, and a very small proportion of the essence of turpentine causes the nature of the electricity to change; the steam in this case becomes negative. Becquerel evidently attri butes the development of the electricity, by the passage of steam under the circumstances recorded in the experiments of 31r. Armstrong, to the friction of the globules of water contained in the steam ; but this interesting question has not yet been examined with sufficient accuracy to allow the formation of any absolute opinions on the subject.
Stcain-Enqine. In conformity with the plan of this Cycloptedia a general outline of the principles of the engine will be here given, the reader being referred to different articles connected with the subject, or to works written specifically on the steam-engine, for more detailed information.
The claim to the invention of the steam-engine has been made a subject of national contention; but the conclusion, arrived at from the discussions which this contention has originated, seems to be, that, in common with all other important applications of physical principles, no individual can lay claim to the invention. Whatever may have end, fitted with a piston 8, and rendered air-tight by having water on it to the depth of several inches : the piston-rod was suspended by a chain from the arched end of a beam c, turning on an axle, and having a pump-rod at its other extremity, loaded so as to counterpoise the weight of the piston, and to raise it to the top of the cylinder. This
cylinder was placed over the boiler D with which it communicated by a steam-pipe E, furnished with a cock r to open or close the passage : o is a cistern fixed above the cylinder, to the bottom of which a pipe n passed, also provided with a cock x.
When the piston was depressed to the bottom of the cylinder, it drove out all tho air before it, which escaped at the orifice of a pipe K into the water of a smaller cistern a : the cock r being next opened, the steam from the boiler filled the cylinder as the piston rose again from the action of the counterpoise; as soon as it arrived at the top, the cock r was closed and I opened, a jet of cold water from the cistern o rushed into the cylinder, condensing the steam, and thus forming a partial vacuum beneath the piston, the pressure of the air on its upper surface forced it downwards, and caused the pump at the other end of the beam to raise an equivalent weight of water to a height equal to that through the piston moved the injected water and con densed steam-water flowed off into the cistern a through K, as the air had previously done. The cock I was now closed, and F opened, and the action was repeated, and when this engine was first introduced, it was the duty of an attendant to open and shut these cocks alternately; but subsequently lever handles to open and shut the cocks were acted on by pins or cams, carried by a rod suspended from a beam ; and the engine became self-acting. This improvement was rudely made in the first instance by a boy named Potter, for the purpose of saving himself trouble; it was subsequently perfected by an engineer named Beigh ton in 1718.
Newcomen's engine was successively improved upon by Smeaton, Brindley, and other engineers, previous to Watt's time, and from its intrinsic merits it remained in general use under the appropriate name of the "atmospheric engine" during the greater part of the last cen tury, but was only used for pumping water.
The first and most important of Watt's improvements on the engine consisted in effecting the condensation in a separate vessel, termed the condenser, which communicated with the cylinder. This condenser being filled with steam from the boiler at the same time with the cylinder, the jet of cold water, admitted into the former only, effected the condensation of the whole volume of steam, both of that in the cylinder as well as of that in the condenser, in conformity with the well-known principle in physics, that an action originated in any part of a homogeneous fluid is almost instantaneously communicated throughout its mass.
To effect still further the object of this separate condensation, Watt placed his condenser in a cistern, the temperature of which was kept constant by a fresh supply of cold water, brought from a well by a pump, to be presently mentioned ; for otherwise, the heat given out by the condensing steam would, by heating the vessel and the water surrounding it, have prevented the rapid or almost instantaneous condensation necessary to the efficient action of the engine.