In the course of his work William was always being faced with
problems caused by the great space taken up by the beam and associated
apparatus of the conventional Watt engine.
This was sunstantially reduced by Watt's own parallel motion, but for
use in steam carraiges or boats the engine's great weight and bulk, and
the instablity given to any vehicle by the consequent high centre of gravity,
made the Watt engine quite impracticle.
The grasshopper type of engine which William dveloped in his first wheel
carraige model was more economical of space but when, in 1785, it occurred
to him to pivot the cylinder at it's base so that it tilted through an
angle of ninety degrees and dispensed with the need for a beam, the space
problem was largely solved and the basic design of the marine engine of
the first thirty years of the nineteenth century was established.
Adapted
from the book "The Third Man" by John Griffiths (1992)