"Alex":
Digressing a bit, I've always wondered why the South coast of England
(mainly the South East) uses the 700V DC "third rail" system for
electrical power, when the entire rest of the UK uses the 25000V AC
overhead cable system. Wouldn't it make more sense to have the same
used all over the UK?

In principle yes, but the Southern network is already pressing the limit
of what is economical as regards both distance and speed for third-rail
trains. Most systems that use it don't have journeys anywhere near as
long as London to Bournemouth or Dover. Low-voltage power requires
frequent substations due to voltage drop, and the amount of current that
can be conveyed is also limited. And if it's DC, it additionally requires
AC-to-DC conversion at every substation.

Besides, wasn't 25kVAC thought up well after 700V DC anyway?

Which completes the story.
--
Mark Brader, Toronto | "When you're up to your ass in alligators, maybe
| you're in the wrong swamp." -- Bill Stewart

My text in this article is in the public domain.