(nights) I'm not totally certain where the term Indian Summer comes from. It may actually be India (from the Raj days) or it may be connected with American Indians. Google has all sorts of theories. Having been a meteorologist, albeit some time ago, I shouldn't have to look it up, of course. It's a bit like a doctor Googling "appendix" and then saying to himself "oh, it's that bit, is it?"
An American Indian summer is very unlikely. The Raj hypothesis is a lot more sensible.. I remember reading the phrase in a PG Wodehouse book, which dates it somewhat, and tends to place it in a Raj-like context rather than an Amercian context.
[Rosie] That's OK. I had a moment in class today where I was explaining about transitive and intransitive verbs, completely forgot which way round they are, and made it up instead. I should know things like that, I'm a bloody linguist.