of a single engine. The cost is much more than an ordinary locomotive, but
the saving in fuel is said to be 20 per cent. over the other engines of
the North Western Rail way. These engines run very sweetly, and are said
to steam freely, although with only half the usual number of blasts; but
from the small size of the high pressure cylinders, they are liable to
slip when starting heavy trains, as the low pressure cylinders are not
then effective, while the consumption of coal does not seem to show the
saving that would have been expected, when compared with ordinary engines
doing similar duty on other lines; for instance, the Great Northern single
engine takes trains of the same weight with the same consumption of coal
and at a somewhat higher speed. But it must, of course, be borne in mind
in making such a comparison, that the fuel used may not be of the same
quality.

Mr. Stirling, of the Great Northern, has adopted an entirely different
type of engine to those last described. Holding strongly that single
engines are more economical not only in running, but in repairs, and that
cylinder power is generally inadequate to the adhesion, he has designed
his magnificent well-known class of express engines. They have single
driving wheels 8 ft. in diameter, with a four-wheel bogie in front and a
pair of trailing wheels, 4 ft. diameter, behind. The frames are single,
and inside of one solid piece; the cylinders are outside 18 in. diameter
and 28 in. stroke; and the valve gear is of the usual shifting link
description. The boiler is of Yorkshire plates, 11 ft. 5 in. long and 4
ft. diameter, and the steam pressure is 140 lb.; while the tractive power
per lb. of steam in the cylinders is 94 lb. The fire-box is of copper, and
the roof is stayed to the outer shell by wrought iron radiating stays
screwed into both; a sloping mid-feather is placed in the fire-box.

[Illustration: FIG. 5.--GREAT NORTHERN RAILWAY.]