t so much in maintaining the machine in
flight as in raising it from the ground. 'When once it is aloft in the
air, the motion of it will be easy, as it is in the flight of all kind
of birds, which being at any great distance from the earth, are able to
continue their motion for a long time and way, with little labour and
weariness.' The right proportion of the wings, both for length and
breadth; the special contrivances necessary for ascent, descent, or a
turning motion--these and many more such questions can only be resolved,
he maintains, by particular experiments. The sails of ships have been
perfected by degrees, and the attempt to fly must meet with many
difficulties and inconveniences for which only long experience and
frequent trial can suggest a remedy.

So far Wilkins went; and he went no farther. His speculations, however,
made a deep impression on his own age, gave a bias to the researches of
his fellows, and, incidentally, aroused a storm of ridicule. When Joseph
Glanvill, in his vigorous little treatise called _Scepsis Scientifica_
(1665), wrote a forecast of the possible achievements of the Royal
Society, he borrowed his hopes from Wilkins. 'Should these heroes go
on', he says, 'as they have happily begun, they will fill the world
with wonders, and posterity will find many things that are now but
rumours, verified into practical realities. It may be, some ages hence,
a voyage to the southern unknown tracts, yea, possibly the Moon, will
not be more strange than one to America. To them that come after us it
may be as ordinary to buy a pair of wings to fly into remotest regions,
as now a pair of boots to ride a journey. And to confer at the distance
of the Indies, by sympathetic conveyances, may be as usual to future
times, as to us in a literary correspondence. The restoration of grey
hairs to juvenility, and renewing the exhausted marrow, may at length be
effected without a miracle; and the turning the now comparative desert
world into a paradise, may not improbably be expected from late
agriculture.' Again, when Sir William Temple, some thirty years later,
cast contempt upon the Moderns in his _Essay of Ancient and Modern
Learning_, it was the speculations of Wilkins that provoked his keenest
satire. 'I have indeed heard of wondrous Pretensions and Visions of Men,
possess'd with Notions of the strange Advancement of Learning and
Sciences, on foot in this Age, and the Progress they are like to make in
the