EXPLANATION OF THE PLATES.
347
PLATE XVIII.
To Boulton and Watt steam navigation is indebted for the effective method of
working two engines jointly, giving, with other advantages, a more equable motion
to the paddle wheel, and, in the event of accident to one of them, enabling the
vessel to proceed with the other at about two-thirds of her greatest velocity.
This plate is an isometrical projection 1 of a steam boat engine, in the manner
they were first arranged by Messrs. Boulton and Watt; and nearly the same
general principle of construction is followed by all the best manufacturers. Two
small engines connected in this way were adapted to the ‘ Prince of Orange ’ and
‘ Princess Charlotte,’ on the Clyde, by these gentlemen, in 1814. Previous to
this, it had been the practice to employ only one engine, ranged by the side of the
boiler, having a fly wheel on the paddle axis to assist the engine in passing its
centres; and in such case the occurrence of any accident immediately put an end
to the progress of the vessel by steam.
The steam comes from the boiler by the pipe' in the front of the figure, and
passes into the steam case and round the cylinder to the slide box, (see art. 146.);
from whence it is let into the cylinder in a manner which will be more clearly
understood by referring to the next plate: from the lower part of the cylinder a
trunk proceeds to the condenser, which is below a square cistern ; beyond which
a part of the air pump is seen, and to the left of it the hot water pump to supply
the boiler.
The motion of the parts commences at the cylinder: the piston rod is supposed
to be descending, and by means of a cross bar (called a cross head) and two side
rods, it depresses the ends of the side beams, these side beams moving on axes in
the centre ; the other ends rise and force a cross bar upwards, to the middle of
which the connecting rod is fixed, by which the crank of the paddle wheel shaft at
the upper part of the figure is turned ; and also by the rising of the further end of
the side beams, the cross head of the air pump and hot water pump is raised by
two side rods. The motion of the piston rod is guided by a combination of rods
called the parallel motion, (see art. 495.) and the slide is moved by an eccentric
1 Some account of this simple and useful mode of drawing, which Avas invented by Professor
Farish, is given in Dr. Gregory’s ‘ Mathematics for Practical Men.’