The steam engine familiarly explained and illustrated; with an historical sketch of its invention and progressive improvement; its applications to navigation and railways; with plain maxims for railway speculators. By the Rev. Dionysius Lardner ... With additions and notes by James Renwick ...

148 THE STEAM ENGINE.
the commencement of the present century, high pressure
engines were altogether neglected in these countries. In the
year 1802, Messrs. Trevithick and Vivian constructed the
first high-pressure engine which was ever brought into extensive practical use in this kingdom. A section of this
machine, made by a vertical plane, is represented in fig. 51.
The boiler A B is a cylinder with flat circular ends. The
fireplace is constructed in the following manner:-A tube
enters the cylindrical boiler at one end; and, proceeding
onward, near the other extremity, is turned and recurved,
so as to be carried back parallel to the direction in which it
entered. It is thus conducted out of the boiler, at another
part of the same end at which it entered. One of the ends
of this tube communicates with the chimney E, which is
carried upward, as represented in the figure. The other
mouth is furnished with a door; and in it is placed the grate,
which is formed of horizontal bars, dividing the tube into
two parts; the upper part forming the fireplace, and the
lower the ash-pit. The fuel is maintained in a state of combustion, on the bars, in that part of the tube represented at
c D; and the flame is carried by the draft of the chimney
round the curved flue, and issues at E into the chimney.
The;flame is thus conducted through the water, so as to
expose the latter to as much heat as possible.
A section of the cylinder is represented at F, immersed in
the boiler, except a few inches of the upper end, where the
four-way cock G is placed for regulating the admission of the
steam. A tube is represented at H. which leads from this
four-way cock into the chimney; so that the waste steam,
after working the piston, is carried off through this tube,
and passes into the chimney. The upper end of the pistonrod is furnished with a cross-bar, which is placed in a direction at right angles to the length of the boiler, and also to
the piston-rod. This bar is guided in its motion by sliding
on two iron perpendicular rods fixed to the sides of the
boiler, and parallel to each other. To the ends of this cross