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
Midland Railway it was found that a coupled engine with ten coaches at
fifty miles an hour made seventeen extra revolutions a mile, but when the
side rods were removed it made forty-three. The Great Western, Great
Northern, and Brighton mainly employ single engines for their fast
traffic; and the Manchester, Sheffield, and Lincolnshire have now adopted
the single type in preference to the coupled for their express trains;
while the North-Western, Midland, South-Western, and Chatham adopted the
coupled type. One noticeable feature in modern practice is the increased
height of the center line of boiler; formerly it was the great aim to keep
this low, and numerous schemes to this effect were propounded, but now it
has become generally recognized that a high pitched engine will travel as
steadily and more safely round a curve--given a good road--than a low
pitched one; and thus while in 1850 the average height of the center line
of boilers varied between 5 ft.
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