I’ve just finished reading the excellent book Caesar's Last Breath: The Epic Story of The Air Around Us I was fascinated by the story about the Siege of Paris which took place in 1870 – 1871 and in particular the story of Pierre Janssen who was the only person allowed to leave the city, in a hot air balloon, to study the sun. He co-discovered helium on these risky ventures! That’s got to be worth a stamp or two.
