wheel tank engine, weighs 48½ tons in working order, it has cylinders 18
in. diameter and 24 in. stroke, and 4 ft. wheels, the boiler pressure is
160 lb., and the tractive force per lb. of mean steam pressure in the
cylinders is 162 lb. This engine will take up the incline twenty-six coal
wagons, or a gross load of 218 tons, which is a very good duty indeed.

Having now passed in review the general types of engines adopted in modern
English practice, the author would briefly draw attention to some points
of design and some improvements effected in late years. And first, as to
the question of single or coupled engines, there is a great diversity of
opinion. Mr. Stirling conducts his traffic at a higher rate of speed, and
certainly with equal punctuality, with his magnificent single 8 ft.
engines, as Mr. Webb on the North-Western with coupled engines, and the
economy of fuel of the former class over the latter is very remarkable;
this is, no doubt, owing, as has been previously pointed out, to their
ample cylinder power, which permits of the steam being worked at a high
rate of expansion. There is no doubt that if single engines can take the
load they will do so more freely and at a less cost than coupled engines,
burning on the average 2 lb. of coal per mile less with similar trains.
With, regard to loads, it is a question whether any express train should
be made up with more than twenty-five coaches. The Great Northern engine
will take twenty-six and keep time, and the Brighton single engine has
taken the five P.M. express from London Bridge to Brighton, consisting of
twenty-two coaches, at a speed of forty-five miles per hour. Of course
where heavy gradients have to be surmounted, such as those on the Midland
route to Scotland, coupled engines are a necessity. Single engines are
said to slip more than coupled; thus an 8 ft. single Great Northern engine
running down the incline from Potter's Bar to Wood Green with twelve
coaches at the rate of sixty miles an hour was found to be making 242
revolutions per mile instead of 210; and in an experiment tried on the