J.B.S. Haldane’s father was a physiologist who would sometimes take his son along while investigating mines in order to teach him the rudiments of science. At one point they were lowered by a bucket into a pit in North Staffordshire, where a tunnel’s low roof forced their party to crawl:

“After a while, we got to a place where the roof was about eight feet high and a man could stand up. One of the party lifted his safety lamp. It filled with blue flame and went out with a pop. If it had been a candle this would have started an explosion, and we should probably have been killed. But of course the flame of the explosion inside the safety lamp was kept in by the wire gauze. The air near the roof was full of methane, or firedamp, which is a gas lighter than air, so the air on the floor was not dangerous.

“To demonstrate the effects of breathing firedamp, my father told me to stand up and recite Mark Anthony’s speech from Shakespeare’s Julius Caesar, beginning ‘Friends, Romans, countrymen.’ I soon began to pant, and somewhere about ‘the noble Brutus’ my legs gave way and I collapsed on to the floor, where, of course, the air was all right. In this way I learnt that firedamp is lighter than air and not dangerous to breathe.”