the damper. If the pressure of the steam rises, the float will be raised
and the damper closed, whereas, if the pressure in the boiler falls, the
reverse of this action will take place.

[Illustration: Fig. 4.]

[Illustration: Fig. 5.]

90. _Q._--Are all land boilers of the same construction as that which you
have just described?

_A._--No; many land boilers are now made of a cylindrical form, with one or
two internal flues in which the furnace is placed. A boiler of this kind is
represented in Figs. 4 and 5, and which is the species of boiler
principally used in Cornwall. In this boiler a large internal cylinder or
flue runs from end to end. In the fore part of this cylinder the furnace is
placed, and behind the furnace a large tube filled with water extends to
the end of the boiler. This internal tube is connected to the bottom part
of the boiler by a copper pipe standing vertically immediately behind the
furnace bridge, and to the top part of the boiler by a bent copper pipe
which stands in a vertical position near the end of the boiler. The smoke,
after passing through the central flue, circulates round the sides and
beneath the bottom of the boiler before its final escape into the chimney.
The boiler is carefully covered over to prevent the dispersion of the heat.

[Illustration: Fig. 6]

91. _Q._--Will you describe the construction of the boilers used in steam
vessels?

_A._--These are of two classes, flue boilers and tubular boilers, but the
latter are now most used. In the flue boiler the furnaces are set within
the boiler, and the flues proceeding from them wind backwards and forwards
within the boiler until finally they meet and enter the chimney. Figs. 6,
7, and 8 are different views of the flue boilers of the steamer Forth.
There are 4 boilers (as shown in plan, Fig. 6), with 3 furnaces in each, or
12 furnaces in all. Fig. 7 is an elevation of 2 boilers, the one to the
right being the front view, and that to the left a transverse section. Fig.
8 is a longitudinal section through 2 boilers. The direction of the arrows
in plan and longitudinal section, will explain the direction of the smoke
current.

[Illustration: Fig. 7.]

[Illustration: Fig. 8.]

92. _Q._--Is this arrangement different from that obtaining in tubular
boilers?

_A._--In tubular boilers, the smoke after leaving the furnace just passes
once through a number of small tubes and then enters the chimney. These
tubes are sometimes