ft. 2 in. outside diameter. The grate area is 17 square feet, and the
heating surface is, tubes, 1,145½ square feet; fire-box 133 square feet;
total, 1,278½ square feet. The boiler pressure is 140 lb. on the square
inch, and the tractive power per lb. of mean pressure in cylinders, 92 lb.
The weight in full working order is, engine, leading wheel, 10 tons; ditto
driving wheels, 14 tons; ditto trailing wheels, 9 tons 10 cwt.; tender,
with 40 cwt. coal and 2,600 gals. water, 26 tons 10 cwt.; total, 60 tons.
These engines are extremely simple, but well proportioned, and are a very
handsome type, and their average consumption of coal, working trains
averaging ten coaches, is about 24.87 lb. per mile. The standard coupled
passenger express engine on the narrow gauge has inside cylinders 17 in.
diameter and 24 in. stroke; the coupled wheels are 6 ft. 6 in. diameter,
and the leading wheels 4 ft.; the wheel base is 16 ft. 9 in. The frames
are double, giving outside bearings to the leading axle, and inside
bearings to the coupled wheels. The boiler is 11 ft. long by 4 ft. 2 in.
diameter; the grate area is 16.25 square feet; and the heating surface is,
tubes, 1,216.5 square feet; fire-box, 97.0 square feet; total, 1,313.5
square feet. The boiler pressure is 140 lb., and the tractive power per
lb. of steam pressure in the cylinders, 88 lb. The weight in full working
order is on the leading wheels, 10 tons 5 cwt.; driving wheels, 11 tons;
trailing wheels, 9 tons 15 cwt.; total, 31 tons.

[Illustration: FIG. 3.--LONDON & NORTH-WESTERN RAILWAY.]

[Illustration: FIG. 4.--JOY'S VALVE GEAR.]

Turning now to the London and North-Western Railway, we find that between
1862 and 1865 the express trains were worked with a handsome type of
engines, known as the "Lady of the Lake" class. They have outside
cylinders 16 in. diameter and 24 in. stroke, with single driving wheels of