The Angle of Incidence would have two Angles and two
Cambers in one, which was manifestly absurd; the Surface
insisted upon no thickness whatever, and would not hear
of such things as Spars and Ribs; and the Thrust objected
to anything at all likely to produce Drift, and very nearly
wiped the whole thing off the Blackboard.

There was, indeed, the makings of a very pretty quarrel
when the Letter arrived. It was about a mile long, and
began to talk at once.

``I'm from the Inventor,'' he said, and hope rose in the
heart of each heated Principle. ``It's really absurdly simple.
All the Pilot has to do is to touch a button, and at his will,
VARY the area of the Surface, the Angle of Incidence,
and the Camber! And there you are--Maximum Climb or
Maximum Speed as required! How does that suit you?''

``That suits us very well,'' said the Surface, ``but, excuse
me asking, how is it done without apparatus increasing the
Drift and the Weight out of all reason? You won't mind
showing us your Calculations, Working Drawings, Stress
Diagrams, etc., will you?''

Said the Letter with dignity, ``I come from an Inventor
so brilliantly clever as to be far above the unimportant
matters you mention. He is no common working man,
sir! He leaves such things to Mechanics. The point is, you
press a button and----''