In 1928 Scottish microbiologist Alexander Fleming, while studying the staphylococcus bacteria, noticed mould on his petri dishes inhibited its growth. He experimented, leading to the discovery of penicillin, the first antibiotic.
In 1945 engineer Percy Spencer, while working on developing a radar system, noticed a chocolate melt very quickly when a new vacuum tube was switched on. He pointed the tube at other objects, which also heated up. This gave rise to the microwave oven.