outset by the problem of constructing a road for heavy locomotives,
with trains of passengers and goods, upon a bog which he had found
incapable of supporting his own weight!

Mr. Stephenson's idea was, that such a road might be made to _float_ upon
the bog, simply by means of a sufficient extension of the bearing
surface. As a ship, or a raft, capable of sustaining heavy loads floated
in water, so in his opinion, might a light road be floated upon a bog,
which was of considerably greater consistency than water. Long before
the railway was thought of, Mr. Roscoe had adopted the remarkable
expedient of fitting his plough-horses with flat wooden soles or pattens,
to enable them to walk upon the Moss land which he had brought into
cultivation. These pattens were fitted on by means of a screw apparatus,
which met in front of the foot and was easily fastened. The mode by
which these pattens served to sustain the horse is capable of easy
explanation, and it will be observed that the _rationale_ likewise
explains the floating of a railway train. The foot of an ordinary
farm-horse presents a base of about five inches diameter, but if this
base be enlarged to seven inches--the circles being to each other as the
squares of the diameters--it will be found that, by this slight
enlargement of the base, a circle of nearly double the area has been
secured; and consequently the pressure of the foot upon every unit of
ground upon which the horse stands has been reduced one half. In fact,
this contrivance has an effect tantamount to setting the horse upon eight
feet instead of four.

Apply the same reasoning to the ponderous locomotive, and it will be
found, that even such a machine may be made to stand upon a bog, by means
of a similar extension of the bearing surface. Suppose the engine to be
20 feet long and 5 feet wide, thus covering a surface of 100 square feet,
and, provided the bearing has been extended by means of cross sleepers
supported on a matting of heath and branches of trees covered with a few
inches of gravel, the pressure of an engine of 20 tons will be only equal
to about 3 pounds per inch over the whole surface on which it stands.
Such was George Stephenson's idea in contriving his floating
road--something like an elongated raft across the Moss; and we shall see
that he steadily kept it in view in carrying the work into execution.

The first thing done was to form a footpath of ling or heather along the
propos