within certain limits. So what I say is, make the surface of
Infinite Span with no width or chord, as they call it. That's
all I require, I assure you, to make me quite perfect and of
infinite service to Miss Efficiency.''

``That's not practical politics,'' said the Surface. ``The
way you talk one would think you were drawing L400 a
year at Westminster, and working up a reputation as an
Aeronautical Expert. I must have some depth and chord
to take my Spars and Ribs, and again, I must have a certain
chord to make it possible for my Camber (that's curvature)
to be just right for the Angle of Incidence. If that's not
right the air won't get a nice uniform compression and
downward acceleration from my underside, and the rarefied
`suction' area over the top of me will not be as even and clean
in effect as it might be. That would spoil the Lift-Drift Ratio
more than you can help it. Just thrust that chalk along, will
you? and the Blackboard will show you what I mean.''

``Well,'' said the Aspect Ratio, ``have it your own way,
though I'm sorry to see a pretty young lady like Efficiency
compromised so early in the game.''

``Look here,'' exclaimed a number of Struts, ``we have
got a brilliant idea for improving the Aspect Ratio,'' and
with that they hopped up on to the Spars. ``Now,'' excitedly,
``place another Surface on top of us. Now do you
see? There is double the Surface, and that being so, the
proportion of Weight to Surface area is halved. That's
less burden of work for the Surface, and so the Spars need