Many things make a noise when you hit them, but not many are commonly used to play music — why is that? Jim Woodhouse looks at harmonic and not so harmonic frequencies and at how percussion instruments are tuned.

How can lives be saved next time the earth moves?

Following on from his article 'The prime number lottery' in last issue of Plus, Marcus du Sautoy continues his exploration of the greatest unsolved problem of mathematics: The Riemann Hypothesis.