Do you remember the first time?

My first science lesson still sticks in my memory some 30-odd years later. After a brief introduction to the importance of observation and experimentation, our teacher weighed some magnesium foil in a small crucible before setting it alight and reweighing the ashes. It had gained weight rather than lost it – quite unexpected to our nine-year-old minds. So we learned that combustion was the result of adding oxygen to the magnesium. Crucially during all this, our teacher insisted that one of us students accompanied him to the balance, to witness the weighing – and make sure he wasn’t cheating. Nullius in verba – take nobody’s word for it – in action.