Can you imagine how Priestley would have conducted the experiment using a candle and a plant? Remember he would need to rekindle the candle to test whether it burns after a few days. How many different ways can you think of to light the candle without disturbing the set-up?

Joseph Priestley performed a series of experiments that revealed the essential role of air in the growth of green plants. He observed that a candle burning in a closed space gets extinguished after some time. Later, he placed a plant into a transparent closed space with a candle that burned out the air until it extinguished. However, after a few days, he rekindle the candle again. At that time, he relied on the sunlight. He focused sunlight beams with a mirror onto the candle wick. The candle relighted successfully without disturbing the experimental setup. This was because of the release of oxygen by the process of photosynthesis. There are different ways to light the candle without disturbing the experimental set up by focusing a light through converging lens or by an electrical spark.