This is the Mill Hill Chapel, and here is where I’ll tell you about the gentleman whose statue you saw at the City Square. His name was Joseph Priestley, and he was the minister here about two centuries ago. He was a Dissenter, meaning a Protestant who worshipped outside the established Church of England. In eighteenth-century England, that mattered. The Church of England was at the centre of religious and social life, while Dissenters could face restrictions and suspicion. Priestley believed Christianity should rest on reason, evidence and the Bible. He rejected the Trinity and believed Jesus was a divinely inspired human being, while questioning original sin and the traditional atonement. In fact, Priestley helped guide this congregation from Presbyterianism towards Unitarianism. He was one of the most inquisitive minds this country has ever produced, and his curiosity extended beyond theology to science, education and politics. In Leeds, he lived near a brewery. But instead of doing the sensible Yorkshire thing and simply enjoying the beer, he became fascinated by the invisible gas bubbling up off the fermenting vats. He worked out how to dissolve that gas into water, and in doing so he invented artificially carbonated water. Every sparkling drink you have ever had, every fizzy lemonade and every overpriced bottle of mineral water, traces back to a curious minister leaning over a brewery vat in Leeds. He won the highest science prize of his day for it, and then, just to show off, he went on to isolate oxygen. The man discovered a component of the air we breathe and the reason soda hisses, which is a fairly good afternoon's work. So next time you crack open something fizzy, you may quietly raise it to Leeds, and to Priestley. Follow the map to the ancient spine of the city.