Where did 625 line television come from?

[Amie]

London TV Station.                                                                                   
  The three stage divider employed to replace the original five stage divider network.
Circuit diagram dated April 1939.

Geordie McBoyne.

Late to the party on this one and a bit OT, but did they really have to use what I assume are a series of charge pump circuits to do service as a divider at the time? ... Respect!