1999 PRATCHETT, T, STEWART, I AND COHEN, J The Science of Discworld. London: Ebury Press.   The wizards of Unseen University create our Universe – accidentally – and take responsibility for the evolution of Roundworld (Earth).

2000 PRATCHETT, T, STEWART, I AND COHEN, J The Science of Discworld 2: The Globe. London: Ebury Press, Random House.  Roundworld (Earth) is infected by elves and the wizards must ensure that Shakespeare is there to sort out the problems – having taught people to decorate caves... 

2005 PRATCHETT, T, STEWART, I AND COHEN, J The Science of Discworld 3: Darwin’s Watch. London: Ebury Press, Random House.  In the Roundworld Victorian Age a country curate called Charles Darwin wrote a very successful book called Theology of Species... and the wizards have to make sure that he takes the Beagle, and writes The Origin of Species instead.