about 230 tons gross. A variation from this type has been adopted on the
Northern and Welsh sections, known as the "Precursor" class. These engines
have 5 ft. 6 in. coupled wheels, and weigh 31 tons 8 cwt. in working
order, but in other respects are very similar to the standard engines just
described; with the Scotch express, averaging in total weight 187 tons,
between Crewe and Carlisle, over heavy gradients, they burn 33 lb. of coal
per mile. These engines, although much more powerful than the standard
type, are not nearly of so handsome an appearance, the drivers seeming
much too small for the boiler under which they are placed. But by far the
boldest innovation on existing practice is the new class of compound
locomotives now being introduced by Mr. Webb. It is a six wheel engine,
with leading wheels 4 ft. diameter, and two pairs of drivers, 6 ft. 6 in.
diameter. The trailing drivers are driven by a pair of outside cylinders,
18 in. diameter and 24 in. stroke; and the leading drivers by a single
low-pressure cylinder--which takes the exhaust steam from the
high-pressure cylinders--of 26 in. diameter and 24 in. stroke, placed
under the center of the smoke-box. The boiler is the same as that in the
standard type of engine, but the wheel base is 17 ft. 7 in., and in order
to allow it to traverse curves easily, the front axle is fitted with a
radial axle-box, which is in one casting from journal to journal, and
fitted at each end with brass steps for the bearings; the box is radial,
struck from the center of the rigid wheel base, and the horn plates are
curved to suit the box, the lateral motion being controlled by strong
springs. Another peculiarity of this engine is that, instead of the
ordinary link motion, it is fitted with Joy's valve gear, which is now
being more and more adopted. This gear--which is of a most ingenious
decription--dispenses altogether with eccentrics, and so allows the inside
bearings to be much increased, those on these engines being 13½ in. long;
and it is also claimed for it that it is simpler and less costly, weighs
less, and is more correct in its action than the ordinary link motion; the