Philo of Byzantium in the second century B.C.E. was the first to observe (or at least the first to record such an observation) that if you placed a jar on top of a candle with water around its base, some water would be drawn up into the jar as the candle burned and eventually went out once all the oxygen was consumed. Although the experiment was well-designed, he ended up with an incorrect conclusion about the process. Robert Boyle repeated the experiment but replaced the candle with a mouse (seriously), and noticed the water also rose up the container. From this experiment he correctly inferred that whatever the component in air was (he called it nitroaerues), it was needed for both combustion and respiration. Robert Hooke, and others, likely produced oxygen gas in the seventeenth century, but didn’t realize it was an element as the phlogiston theory (see below) was in vogue at the time. So to really realize that oxygen gas was required for fire, it first had to be, well, discovered.