The Science of Discworld IV

BY THE SAME AUTHORS
    TERRY PRATCHETT
The Discworld ® series
    THE COLOUR OF MAGIC • THE LIGHT FANTASTIC • EQUAL RITES • MORT • SOURCERY • WYRD SISTERS • PYRAMIDS • GUARDS! GUARDS! • ERIC (illustrated by Josh Kirby) • MOVING PICTURES • REAPER MAN • WITCHES ABROAD • SMALL GODS • LORDS AND LADIES • MEN AT ARMS • SOUL MUSIC • INTERESTING TIMES • MASKERADE • FEET OF CLAY • HOGFATHER • JINGO • THE LAST CONTINENT • CARPE JUGULUM • THE FIFTH ELEPHANT • THE TRUTH • THIEF OF TIME • THE LAST HERO (illustrated by Paul Kidby) • THE AMAZING MAURICE AND HIS EDUCATED RODENTS (for younger readers) • NIGHT WATCH • THE WEE FREE MEN (for younger readers) • MONSTROUS REGIMENT • A HAT FULL OF SKY (for younger readers) • GOING POSTAL • THUD • WINTERSMITH (for younger readers) • MAKING MONEY • UNSEEN ACADEMICALS • I SHALL WEAR MIDNIGHT (for younger readers) • SNUFF
    The Science of Discworld series
(with Ian Stewart and Jack Cohen)
    THE SCIENCE OF DISCWORLD
    THE SCIENCE OF DISCWORLD II: THE GLOBE
    THE SCIENCE OF DISCWORLD III: DARWIN’S WATCH
    Other books about Discworld
    TURTLE RECALL: THE DISCWORLD COMPANION … SO FAR
(with Stephen Briggs)
    NANNY OGG’S COOKBOOK
(with Stephen Briggs, Tina Hannan and Paul Kidby)
    THE PRATCHETT PORTFOLIO (with Paul Kidby)
    THE DISCWORLD ALMANAK (with Bernard Pearson)
    THE UNSEEN UNIVERSITY CUT-OUT BOOK
(with Alison Batley and Bernard Pearson)
    WHERE’S MY COW? (illustrated by Melvyn Grant)
    THE ART OF DISCWORLD (with Paul Kidby)
    THE WIT AND WISDOM OF DISCWORLD (compiled by Stephen Briggs)
    THE FOLKLORE OF DISCWORLD (with Jacqueline Simpson)
    MISS FELICITY BEEDLE’S THE WORLD OF POO
(assisted by Bernard and Isobel Pearson)
    Discworld Maps and Gazetteers
    THE STREETS OF ANKH-MORPORK
(with Stephen Briggs, painted by Stephen Player)
    THE DISCWORLD MAPP (with Stephen Briggs, painted by Stephen Player)
    A TOURIST GUIDE TO LANCRE – A DISCWORLD MAPP
(with Stephen Briggs, illustrated by Paul Kidby)
    DEATH’S DOMAIN (with Paul Kidby)
    THE COMPLEAT ANKH-MORPORK (with the Discworld Emporium)
    A complete list of Terry Pratchett ebooks and audio books as well as other books based on the Discworld series – illustrated screenplays, graphic novels, comics and plays – can be found on www.terrypratchett.co.uk
    Non-Discworld books
    THE DARK SIDE OF THE SUN • STRATA
    THE UNADULTERATED CAT (illustrated by Gray Jolliffe)
    GOOD OMENS (with Neil Gaiman)
    THE LONG EARTH (with Stephen Baxter)
    A BLINK OF THE SCREEN: COLLECTED SHORT FICTION
    Non-Discworld novels for younger readers
    THE CARPET PEOPLE • TRUCKERS • DIGGERS • WINGS • ONLY YOU CAN SAVE MANKIND • JOHNNY AND THE DEAD • JOHNNY AND THE BOMB • NATION • DODGER
    Ian Stewart
    CONCEPTS OF MODERN MATHEMATICS • GAME, SET, AND MATH • DOES GOD PLAY DICE? • ANOTHER FINE MATH YOU’VE GOT ME INTO • FEARFUL SYMMETRY • NATURE’S NUMBERS • FROM HERE TO INFINITY • THE MAGICAL MAZE • LIFE’S OTHER SECRET • FLATTERLAND • WHAT SHAPE IS A SNOWFLAKE? • THE ANNOTATED FLATLAND • MATH HYSTERIA • THE MAYOR OF UGLYVILLE’S DILEMMA • HOW TO CUT A CAKE • LETTERS TO A YOUNG MATHEMATICIAN • TAMING THE INFINITE (alternative title: THE STORY OF MATHEMATICS) • WHY BEAUTY IS TRUTH • COWS IN THE MAZE • MATHEMATICS OF LIFE • PROFESSOR STEWART’S CABINET OF MATHEMATICAL CURIOSITIES • PROFESSOR STEWART’S HOARD OF MATHEMATICAL TREASURES • SEVENTEEN EQUATIONS THAT CHANGED THE WORLD (alternative title: IN PURSUIT OF THE UNKNOWN)
    JACK OF ALL TRADES (science fiction ebook)
    THE GREAT MATHEMATICAL PROBLEMS
(alternative title: VISIONS OF INFINITY)
    SYMMETRY: A VERY SHORT INTRODUCTION
    Jack Cohen
    LIVING EMBRYOS • REPRODUCTION • PARENTS MAKING PARENTS • SPERMS, ANTIBODIES AND INFERTILITY • THE PRIVILEGED APE
    STOP WORKING AND START THINKING (with Graham Medley)
    Jack Cohen and Ian Stewart
    THE COLLAPSE OF CHAOS
    EVOLVING THE ALIEN
(alternative title: WHAT DOES A MARTIAN LOOK LIKE?)
    Ian Stewart and Jack Cohen
    FIGMENTS OF REALITY
    WHEELERS (science fiction) • HEAVEN (science fiction)



PROLOGUE
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WORLDS, DISC AND ROUND

    There is a sensible way to make a world.
    It should be flat, so that no one falls off accidentally fn1 unless they get too near the edge, in which case it’s their own fault.
    It should be circular, so that it can revolve sedately to create the slow progression of the seasons.
    It should have strong supports, so that it doesn’t fall