with a machine in horizontal translation, is impossible,
unless it is done by taking into account
the factor due to momentum and the element
attributable to the lift of the plane itself due to its
impact against the atmosphere.

LANGLEY'S LAW.--The law enunciated by
Langley is, that the greater the speed the less the
power required to propel it. Water as a propelling
medium has over seven hundred times
more force than air. A vessel having, for instance,
twenty horse power, and a speed of ten
miles per hour, would require four times that
power to drive it through the water at double the
speed. The power is as the square of the speed.

With air the conditions are entirely different.
The boat submergence in the water is practically
the same, whether going ten or twenty miles an
hour. The head resistance is the same, substantially,
at all times in the case of the boat; with the
flying machine the resistance of its sustaining
surfaces decreases.

Without going into a too technical description
of the reasoning which led to the discovery of the
law of air pressures, let us try and understand
it by examining the diagram, Fig. 7.

A represents a plane at an angle of 45 degrees,