The Fleet continues to wind its way north, ending up at Hampstead Heath, the ponds of which were actually formed by a damming of the river in the 18th Century.

BBC: In search of London's lost rivers

These are the batteries that go into electric cars, or the batteries that are ending up helping to make sure that if you get solar power or wind power, that it can be transmitted in an efficient way.

WHITEHOUSE: The Economy and the American Family