was 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 of energy necessary to set such heavy
wheels spinning at a high velocity. The last experiment with these
wheels was made when a head wind was blowing at the rate of about ten
miles an hour. It was rather unsteady, and when the machine was running
at its greatest velocity, a sudden gust lifted not only the front
end, but also the heavy front wheels completely off the track, and the
machine falling on soft ground was soon blown over by the wind.'

Consequently, a safety track was provided, consisting of squared pine
logs, three inches by nine inches, placed about two feet above the steel
way and having a thirty-foot gauge. Four extra wheels were fitted to the
machi