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,