provided, and had all the auxiliary planes been put in position
for experimental work a total lifting surface of 6,000 square
feet could have been obtained. Maxim, however, did not use more
than 4,000 square feet of lifting surface even in his later
experiments; with this he judged the machine capable of lifting
slightly under 8,000 lbs. weight, made up of 600 lbs. water in
the boiler and tank, a crew of three men, a supply of naphtha
fuel, and the weight of the machine itself.

Maxim's intention was, before attempting free flight, to get as
much data as possible regarding the conditions under which
flight must be obtained, by what is known in these days as
'taxi-ing'--that is, running the propellers at sufficient speed
to drive the machine along the ground without actually mounting
into the air. He knew that he had an immense lifting surface
and a tremendous amount of power in his engine even when the
total weight of the experimental plant was taken into
consideration, and thus he set about to devise some means of
keeping the machine on the nine foot gauge rail track which had
been constructed for the trials. At the outset he had a set of
very heavy cast-iron wheels made on which to mount the machine,
the total weight of wheels, axles, and connections being about
one and a half tons. These were so constructed that the light
flanged wheels which supported the machine on the steel rails
could be lifted six inches above the track, still leaving the
heavy wheels on the rails for guidance of the machine. 'This
arrangement,' Maxim states, 'was tried on several occasions, the
machine being run fast enough to lift the forward end off the
track. However, I found considerable difficulty in starting and
stopping quickly on account of the great weight, and the amount