eans of engine power
would be mostly confined to the construction of navigable balloons.

As already noted, Walker's work is not over practical, and the foregoing
extract includes the most practical part of it; the rest is a series
of dissertations on bird flight, in which, evidently, the portrait
painter's observations were far less thorough than those of da Vinci or
Borelli. Taken on the whole, Walker was a man with a hobby; he devoted
to it much time and thought, but it remained a hobby, nevertheless. His
observations have proved useful enough to give him a place among the
early students of flight, but a great drawback to his work is the lack
of practical experiment, by means of which alone real advance could
be made; for, as Cayley admitted, theory and practice are very widely
separated in the study of aviation, and the whole history of flight is
a matter of unexpected results arising from scarcely foreseen causes,
together with experiment as patient as daring.

IV. THE MIDDLE NINETEENTH CENTURY

Both Cayley and Walker were theorists, though Cayley supported his
theoretical work with enough of practice to show that he studied along
right lines; a little after his time there came practical men
who brought to being the first machine which actually flew by the
application of power. Before their time, however, mention must be made
of the work of George Pocock of Bristol, who, somewhere about 1840
invented what was described as a 'kite carriage,' a vehicle which
carried a number of persons, and obtained its motive power from a large
kite. It is on record that, in the year 1846 one of these carriages
conveyed sixteen people from Bristol to London. Another device of
Pocock's was what he called a 'buoyant sail,' which was in effect a
man-lifting kite, and by means of which a passenger was actually raised
100 yards from the ground, while the inventor's son scaled a cliff
200 feet in height by means of one of these, 'buoyant sails.' This
constitutes the first definitely recorded experiment in the use of
man-lifting kites. A History of the Charvolant or Kite-carriage,
published in London in 1851, states that 'an experiment of a bold and
very novel character was made upon an extensive down, where a large
wagon with a considerable load was drawn along, whilst this huge machine
at the same time carried an observer aloft in the air, realising almost
the romance of flying.'

Experimenting, two years after the appearance o