Overview: The Sea Eagles of the island of Canna were hunted to extinction, but now they have been brought back. We climb into one of their nests perched high on a steep cliff to find out what their chances of survival are. Neil Oliver visits Europe's biggest super-quarry to receive an explosive lesson in how the rock is mined. Armed with a simple ruler on a Scottish beach, Nick Crane learns how the challenge of measuring our coastline led to a new branch of maths that could help our mobile phones get smaller.