The scene: a nondescript
service station in a nondescript town somewhere in central California.
We have stopped here for tea and petrol. Michael and I, dressed in boots,
jodhpurs, flight jackets and white silk scarves, goggles pushed up over
our tousled hair, have unbuckled the strap and folded back the louvered
bonnet to appraise and admire, respectively, the gleaming innards of
the silver and grey Morgan +4.
Michael: [technical
discussion picked up in progress]...the speedometers been reading
50 mph, but we've actually been travelling 10 to 15 mph faster than
that.
Me: Oh yeah? How
do you figure?
Michael: [insert
incompletely understood explanation of gear ratios here] therefore,
in top gear at 33-1/3 rpm we're actually going about 60 mph. The odometer
is similarly configured--it shows fewer miles than we've actually travelled.
Me: I see. So if
the speedometer shows x miles per hour over y hours, when we're actually
travelling at z miles per hour, the odometer should read zy miles instead
of xy miles, a number that can be calculated from the actual odometer
reading assuming a) we are able to determine y with sufficient precision
and b) we are able to determine the relationship between z and x, the
equation for which is linear but dependent on which gear the car is
in....
Michael: Which
is, of course, dependent on the cars speed.
Me: Precisely.
At this point we
agreed that an onboard Babbage engine would be of inestimable benefit
to the motoring public. Where to put it was somewhat problematic due
to space constraints but I recalled that this design challenge had somehow
been met by Lord Julian Spagthorpe in the Spagthorpe Wolfhound, and
that if we were fortunate we might spot one at the rally and possibly
discuss the situation with its owner. Elated at the possibility of contributing
to such a milestone in British automotive engineering, we folded the
bonnet into place, strapped it down, shoehorned ourselves back into
the car and set off for the south at some unknown but theoretically
calculable speed.
Lady Jilian Spagthorpe
Spagthorpe Motorcycle Company