The Central London Railway began with Camel Backed Electric
locomotives hauling unpowered carriages. In order to improve
efficiency distinct humps (mini summits) were built into the track
profile at stations from Notting Hill to Liverpool Street ...

I think it was an innovation on the Central London Railway wasn't it,

No.

with the earliest lines not having it?

The subsurface lines didn't do it; the cost of a cut-and-cover tunnel
increases with depth. Tubes are another matter, and the first deep
tube line, the City & South London Railway of 1890, did do it. (The
part of this line still in use today is from Stockwell to near Borough
on the Northern Line.)

I don't have exact details on all the humps, but the book on the C&SLR
by T.S. Lascelles says that "at most but not all stations there was
a short down grade of about 1 in 30 to assist trains in accelerating",
while Jackson and Croome in "Rails Through the Clay" say that "where
possible, intermediate stations were built on humps".
--
Mark Brader | "The job of an engineer is to build systems that
Toronto | people can trust. By this criterion, there
| exist few software engineers." --John Shore

My text in this article is in the public domain.