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 of brass, and they are usually about 3 inches in
diameter, and 6 or 7 feet long.

[Illustration: Fig. 9.]

[Illustration: Fig. 10.]