During the Christmas holidays of 1825, the Royal Institution organised a short programme of science lectures for young people. This became an annual event, which continues today. For the 1848 season, Michael Faraday gave a series of six talks called The Chemical History of a Candle. They were published in book form in 1861, soon after Faraday had repeated the series for Christmas 1860.

Ernest Hemingway once said that someone starting a book should write down the truest sentence they know and work out from there. In this beguiling series of lectures, with visual illustration from experiments involving heat, cold, balloons, explosion and implosion, Faraday explores the physics and chemistry of a candle, which he presents as a tiny model for more general processes. In effect, he follows Hemingway’s advice, taking a candle as the truest of things and working outwards. I now know that candle wax is what’s called a hydrocarbon, a substance consisting of hydrogen and carbon in combination. Lighting a candle wick causes the wax to melt and vaporise into a hot gas. This causes the hydrocarbons to start breaking down into their constituent parts of hydrogen and carbon, which are drawn up into the flame. Here they combine with oxygen in the air to produce water (hydrogen and oxygen) and carbon dioxide (carbon and oxygen). Candle combustion is basically the same as any combustion anywhere, including that driving life. As I write this review, and as you read it, we breath in atmospheric oxygen to fan our metabolic flame, breaking down food hydrocarbons to produce energy and heat, with water vapour and carbon dioxide as by-products, which we breathe out.

Faraday takes apart the process of candle burning, and the products that result, demonstrating many clever techniques of division. Fascinatingly though, Faraday doesn’t simply take things apart, but also shows them acting together as a whole. For example, he makes reference to nitrogen in the atmosphere, an abundant gas that actually suppresses burning. How does a fire suppressant gas contribute to the process of combustion? Well, an atmosphere of oxygen alone would produce an explosive, tinderbox world. Nitrogen alone would make it impossible to support the combustion that supports life. An atmosphere of oxygen existing alongside a larger proportion of nitrogen, allows a candle to burn in a controlled way for hours. I found myself considering life in these terms. There are many circumstances holding us back from shining our various lights, more problems than solutions no doubt. Although nitrogen is the dominant gas, in combination with a little oxygen, we have the chance to burn with a steady flame.

The lectures do invite this sort of thinking, the penultimate lecture encouraging the audience to consider themselves as candles and spread some illumination around.

This book was a delightful surprise. It turns out that a candle is one of the truest things I know.