used for the
purpose of quickening combustion in the furnace, were worked off the same
crank-axle.

John Petherick, of Camborne, has related that he remembers this first
English steam-coach passing along the principal street of his native
town. Considerable difficulty was experienced in keeping up the pressure
of steam; but when there was pressure enough, Trevithick would call upon
the people to "jump up," so as to create a load upon the engine. It was
soon covered with men attracted by the novelty, nor did their number seem
to make any difference in the speed of the engine so long as there was
steam enough; but it was constantly running short, and the horizontal
bellows failed to keep it up.

This road-locomotive of Trevithick's was one of the first high-pressure
working engines constructed on the principle of moving a piston by the
elasticity of steam against the pressure only of the atmosphere. Such an
engine had been described by Leopold, though in his apparatus it was
proposed that the pressure should act only on one side of the piston. In
Trevithick's engine the piston was not only raised, but was also
depressed by the action of the steam, being in this respect an entirely
original invention, and of great merit. The steam was admitted from the
boiler under the piston moving in a cylinder, impelling it upward. When
the motion had reached its limit, the communication between the piston
and the under side was shut off, and the steam allowed to escape into the
atmosphere. A passage being then opened between the boiler and the upper
side of the piston, which was pressed downwards, the steam was again
allowed to escape as before. Thus the power of the engine was equal to
the difference between the pressure of the atmosphere and the elasticity
of the steam in the boiler.

This steam-carriage excited considerable interest in the remote district
near the Land's End where it had been erected. Being so far removed from
the great movements and enterprise of the commercial world, Trevithick
and Vivian determined upon exhibiting their machine in the metropolis.
They accordingly set out with it to Plymouth, whence it was conveyed by
sea to London.

The carriage safely reached the metropolis, and excited much public
interest. It also attracted the notice of scientific men, amongst others
of Mr. Davies Gilbert, President of the Royal Society, and Sir Humphry
Davy, both Cornishmen like Trevithick, who went to see the