ch an engine is entirely
practicable. Indeed, working motors of one-half this weight per
horse-power (9 lbs. per horse-power) have been constructed by several
different builders. Increasing the speed of our machine from 24 to 33
miles per hour reduced the total horizontal pressure from 40 to about 35
lbs. This was quite an advantage in gliding, as it made it possible to
sail about 15 per cent farther with a given drop. However, it would
be of little or no advantage in reducing the size of the motor in
a power-driven machine, because the lessened thrust would be
counterbalanced by the increased speed per minute. Some years ago
Professor Langley called attention to the great economy of thrust which
might be obtained by using very high speeds, and from this many were led
to suppose that high speed was essential to success in a motor-driven
machine. But the economy to which Professor Langley called attention was
in foot pounds per mile of travel, not in foot pounds per minute. It
is the foot pounds per minute that fixes the size of the motor. The
probability is that the first flying machines will have a relatively low
speed, perhaps not much exceeding 20 miles per hour, but the problem of
increasing the speed will be much simpler in some respects than that of
increasing the speed of a steamboat; for, whereas in the latter case the
size of the engine must increase as the cube of the speed, in the flying
machine, until extremely high speeds are reached, the capacity of the
motor increases in less than simple ratio; and there is even a decrease
in the fuel per mile of travel. In other words, to double the speed of
a steamship (and the same is true of the balloon type of airship) eight
times the engine and boiler capacity would be required, and four times
the fuel consumption per mile of travel: while a flying machine would
require engines of less than double the size, and there would be an
actual decrease in the fuel consumption per mile of travel. But looking
at the matter conversely, the great disadvantage of the flying machine
is apparent; for in the latter no flight at all is possible unless the
proportion of horse-power to flying capacity is very high; but on
the other hand a steamship is a mechanical success if its ratio of
horse-power to tonnage is insignificant. A flying machine that would fly
at a speed of 50 miles per hour with engines of 1,000 horse-power would
not be upheld by its wings at all at a speed of less than