d all the wheels were running on the upper
track, and revolving in the opposite direction from those on the lower
track. However, after running about 1,000 feet, an axle tree doubled up,
and immediately afterwards the upper track broke away, and the machine,
becoming liberated, floated in the air, "giving those on board a
sensation of being in a boat."

The experiment proved conclusively to the inventor that a machine
could be made on a large scale, in which the lifting effect should be
considerably greater than the weight of the machine, and this, too,
when a steam engine was the motor. When, therefore, in the years shortly
following, the steam engine was for the purposes of aerial locomotion
superseded by the lighter and more suitable petrol engine, the
construction of a navigable air ship became vastly more practicable.
Still, in Sir H. Maxim's opinion, lately expressed, "those who seek
to navigate the air by machines lighter than the air have come,
practically, to the end of their tether," while, on the other hand,
"those who seek to navigate the air with machines heavier than the air
have not even made a start as yet, and the possibilities before them are
very great indeed."

As to the assertion that the aerial navigators last mentioned "have not
even made a start as yet," we can only say that Sir H. Maxim speaks with
far too much modesty. His own colossal labours in the direction of that
mode of aerial flight, which he considers to be alone feasible, are
of the first importance and value, and, as far as they have gone,
exhaustive. Had his experiments been simply confined to his classical
investigations of the proper form of the screw propeller his name would
still have been handed down as a true pioneer in aeronautics. His work,
however, covers far wider ground, and he has, in a variety of ways,
furnished practical and reliable data, which must always be an
indispensable guide to every future worker in the same field.

Professor Langley, in attacking the same problem, first studied the
principle and behaviour of a well-known toy--the model invented by
Penaud, which, driven by the tension of india-rubber, sustains itself in
the air for a few seconds. He constructed over thirty modifications of
this model, and spent many months in trying from these to as certain
what he terms the "laws of balancing leading to horizontal flight." His
best endeavours at first, however, showed that he needed three or four
feet of su