, being considered an adjunct to fairs and fetes, more a pastime
than a study.

Up to the time of his death, in 1857, Cayley maintained his study of
aeronautical matters, and there is no doubt whatever that his work
went far in assisting the solution of the problem of air conquest. His
principal published work, a monograph entitled Aerial Navigation, has
been republished in the admirable series of 'Aeronautical Classics'
issued by the Royal Aeronautical Society. He began this work by
pointing out the impossibility of flying by means of attached wings, an
impossibility due to the fact that, while the pectoral muscles of a bird
account for more than two-thirds of its whole muscular strength, in a
man the muscles available for flying, no matter what mechanism might be
used, would not exceed one-tenth of his total strength.

Cayley did not actually deny the possibility of a man flying by muscular
effort, however, but stated that 'the flight of a strong man by great
muscular exertion, though a curious and interesting circumstance,
inasmuch as it will probably be the means of ascertaining finis power
and supplying the basis whereon to improve it, would be of little use.'

From this he goes on to the possibility of using a Boulton and Watt
steam engine to develop the power necessary for flight, and in this he
saw a possibility of practical result. It is worthy of note that in
this connection he made mention of the forerunner of the modern internal
combustion engine; 'The French,' he said, 'have lately shown the great
power produced by igniting inflammable powders in closed vessels,
and several years ago an engine was made to work in this country in
a similar manner by inflammation of spirit of tar.' In a subsequent
paragraph of his monograph he anticipates almost exactly the
construction of the Lenoir gas engine, which came into being more than
fifty-five years after his monograph was published.

Certain experiments detailed in his work were made to ascertain the
size of the surface necessary for the support of any given weight.
He accepted a truism of to-day in pointing out that in any matters
connected with aerial investigation, theory and practice are as
widely apart as the poles. Inclined at first to favour the helicopter
principle, he finally rejected this in favour of the plane, with which
he made numerous experiments. During these, he ascertained the peculiar
advantages of curved surfaces, and saw the necessity of pr