Because the earth is a sphere, the
shortest distance between any two points on it must be a curve.
This can be seen if one stretches a cord between two places on a
globe; the stretched cord will lie along the 'great circle' linking
the two places. (A 'great circle' is one that encircles the globe,
its diameter being the diameter of the globe.) John Thomas Towson,
who was scientific examiner of masters and mates at Liverpool, saw
the advantages of a great circle route to Australia years before
the gold rush. He knew full well, however, that it was impossible
to keep to a great circle all the way from the South Atlantic to
Australia, for such a route led into Antarctica; in any event, a
curved route could not be followed by ships' compasses. His answer
was a break-up of a curved route into a series of chords, or 'rhumbs',
going as far south as ice would allow. Such a route cut out Cape
Town completely, leaving it hundreds of miles to the north.
Towson presented his calculations in 1847 in a small but radical
book: Tables to Facilitate the Practice of Great Circle Sailing
and Determination of Azimuths.
• from The Long Farewell by