Three more teams make their challenge for the Royal Institution trophy. Presented by Paddy Feeny Heat 2
LEICESTER: attempting to crack the secret of a commercial water softener.
KESWICK: trying to solve the mysteries of a 4,000-year-old stone circle.
TREGARON: undertaking a ye*r-long study into the effects of the sodium fallout on Tregaron Bog. Judging their work:
PROF IAN FELLS , fuel scientist
PROF COLIN RENFREW , archaeologist PROF TONY BRADSHAW , botanist
Studio director JOHN GORMAN Producer PETER BRUCE