Science series. Like a large elastic ball, the Earth has an element of flexibility. Quentin Coopertalks to Dr Peter Clarke and Dr Paul Cruddace who are about to start surveying the level of "bounce" in the UK. Using more than 30 global-positioning satellite receivers with millimetre accuracy, they hope to record a daily rise and fall of about 10 centimetres. Will theirfindings have a profound effect on large construction projects like the Channel tunnel? Producer Fiona Roberts. E-MAIL: material.world@bbc.co.uk