On holiday in Italy, but thinking of Brunel. The London tube holds no fears for me, but tunnels under the Alps are just a bit too long for complete peace of mind. This was a sensation entirely familiar to people travelling through Brunel’s tunnels: by foot under the Thames, or by Great Western Railway under Box. One of Brunel’s eccentric detractors, Professor Dionysus Lardner, argued passionately about the dangers of travelling at high speed through tunnels. Box was the longest railway tunnel in the world, and Lardner explained to a terrified audience that the air would be travelling too fast to be breathed. In the strangest of railway accidents, passengers would arrive intact, but lifeless. Less confident travellers always left the train at Bath and jolted down to Bristol by carriage. Except ‘jolt’ does not amply describe what early travellers went through: in Jane Austen’s famous description of the picnic at Box, our heroine arrives by carriage ‘entirely knocked up.’ But at least the air was respirable.