er and by several vertical water-tubes of less
diameter. In the "Victoria" boiler made by Messrs Clarke, Chapman &
Co., and illustrated in fig. 6, the furnace is hemispherical; the
furnace gases are led to an internal combustion chamber, and thence
through numerous horizontal smoke-tubes to a smoke-box placed on the
side of the boiler. In the somewhat similar boiler known as the
"Cochran," the combustion chamber is made with a "dry" back. Instead
of a water space at the back of the chamber, doors lined with
firebrick are fitted. These give easy access to the tube ends.

[Illustration: FIG. 3.--Lancashire Boiler.]

[Illustration: FIG. 4.--Simple Vertical Boiler (Messrs Tinker, Ltd.).]

Marine.

The cylindrical multitubular return tube boiler is in almost universal
use in merchant steamers. It is made in various sizes ranging up to 17
ft. in diameter, the usual working pressure being from 160 to 200 lb
per sq. in., although in some few cases pressures of 265 lb. per sq.
in. are in use. These boilers are of two types, double- and
single-ended. In single-ended boilers, which are those most generally
used, the furnaces are fitted at one end only and vary in number from
one in the smallest boiler to four in the largest. Three furnaces are
the most usual practice. Each furnace generally has its own separate
combustion chamber. In four furnace boilers, however, one chamber is
sometimes made common to the two middle furnaces, and sometimes one
chamber is fitted to each pair of side furnaces. In double-ended
boilers furnaces are fitted at each end. In some cases each furnace
has a separate combustion chamber, but more usually one chamber is
made to serve for two furnaces, one at each end of the boiler. The two
types of boilers are shown in figs. 7 and 8, which illustrate boilers
made by Messrs D. Rowan & Co. of Glasgow, and which may be taken as
representing good modern practice. The furnaces used in the smaller
sizes are often of the plain cylindrical type, the thickness of plate
varying from 3/8 in. up to 3/4 in. according to the diameter of the
furnace and the working pressure. Occasionally furnaces with "Adamson"
joints similar to those used in Lancashire boilers are employed, but
for large furnaces and for high pressures corrugated or ribbed
furnaces are usually adopted. Sketches of the sections of these are
shown in fig. 9. The sections of the Mo