wrote to uk.transport.london on Fri, 17 Jun 2005:

One evening in 1964 I was at the Victoria end of the island platform at
Streatham Common, and I could see (and hear!) some kind of PUL/PAN
formation approaching at speed on the down fast. It was belting along.
It was always satisfactory to be on the platform when they rushed
through. As the train came into view, I could not help noticing (it was
dark) that each shoe on the juice rail side was making its own little
shower of sparks. They were yellow-orange rather than blue, and I
wondered if they were caused by brief loss of contact due to the
swaying bouncy ride these sets had especially at speed.

My father, in the very late 1950s/early 1960s commuted to London from
the Sussex coast. Although it wasn't, and isn't, his nearest station,
he invariably went from Arundel on the mid-Sussex line (still utterly
delightful, and incredibly pretty south of Horsham), which in those days
called at Pulborough, Horsham, Dorking North, Epsom, Sutton & Victoria -
we nearly always travelled the same way when visiting my grandmother in
London. On the rare occasions we went via the Brighton lines, there
were always showers of sparks and blue flashes - my father told me,
years later, that it wasn't just the beauty of the mid-Sussex that
attracted him, but the fact that the trains on that line had "less
square wheels" than those on the Brighton run!
--
"Mrs Redboots"
http://www.amsmyth.demon.co.uk/
Website updated 23 May 2005