Your correspondence on quantum mechanics (Editorial 30 August; Letters 3 September) brought back memories of a conversation I had with a German biologist 50 years ago. He explained that he wanted to become a theoretical physicist as a teenager and attended a lecture on Wolfgang Pauli's exclusion principle. Pauli was able to see the end of his lecture and said, "That was amazing, I could see exactly how you meant."
Professor John Galloway
Croxley Green, Hertfordshire
Richard Walker (Letters 3 September) has the right idea about Crossroads TV's theme. I have always felt that certain programmes are more popular than they deserve purely due to their theme tune. Van der Valk's 1970s detective series was a clear candidate, thanks to its excellent theme tune, Eye Level.
Dougie Mitchell
Edinburgh
Concerning weather forecasts (Letters 2 September), I was reminded by the words of an American friend who visited in the 1980s. He said that he didn't understand why Brits care about weather forecasts. The UK has only three weather states: it's just stopped raining or its raining, and it's just about to start raining.
Ray Woodhams
Barnsley, South Yorkshire
Simon Jenkins claims that the Afghan war cost Britain 37.5 billion. (Biden wasn't the first president not to pledge to never wage another war of aggression, 3 September). This is the exact amount Boris Johnson gave to NHS trace and test (provided privately). It is amazing.
Jeanne Warren
Oxford
