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A little over 350 years ago, on the night between Saturday 1 and Sunday 2 September 1666, Thomas Farynor, well-known baker, lay in bed in his home above his bakery. Maybe he was staring at the ceiling, worrying, as he did every night, as to whether he had completely put out the fire in his ovens. Or maybe he was just asleep. It had, after all, been a long day.

But today was not yet over. The ovens, you see, weren’t dead: somewhere, there was a mortal red glow, the glow gave birth to a flickering flame and before he knew it, Thomas Farynor had escaped with his family through an upstairs window, his maid had decided she was more afraid of heights than fire and London was aflame. In the course of the next four days, it destroyed 13,200 houses, 87 churches (including St Paul’s Cathedral) and much more. Samuel Pepys, the superior version of Bridget Jones, ran around burying his parmesan cheese and looking at “the houses at the end of the bridge all on fire, and an infinite great fire on this and the other side […] of the bridge”.

Eventually, thanks in part to the intentional destruction of buildings to stop the spread of the fire (the standard fire-fighting technique of the time), the Great Fire of London petered out. Following an Act of Parliament, a monument (unimaginatively called Monument) was erected “the better to preserve the memory of this dreadful visitation”. What is less known, however, is that Monument is actually an enormous scientific instrument.

Wren’s friend

Although most commonly attributed to Sir Christopher Wren, who re-designed much of London following the fire, the design of Monument was actually due to a friend of his from their Oxford days: Robert Hooke, possibly the most neglected of the great English scientists. Famous today for his eponymous law, which says that the tension in a spring is linearly proportional to its extension, he also did amazing work in acoustics, biology, geology, microscopy, palaeontology and philosophy; proposed a revolutionary model, far removed from the philosophical musings of the time, “explaining the organ of memory”; published a theory of light that suggested that it propagated as a wave; found that matter expanded when it was heated; discovered… . Sadly, much of what he accomplished was either forgotten or, like Monument, misattributed.

His many and varied interests meant that he was an excellent choice for Curator of Experiments at the Royal Society. This role involved designing and performing experiments at meetings of the society, probably the most bizarre of which saw him cut open the chest of a dog to prove that it could stay alive on the condition that air be pumped in and out of its lungs. However, it was his job as Surveyor to the City of London, coupled with both his and Wren’s fascination with astronomy, that turned a monument to a fire into a giant telescope.

How to obtain funding for science

Monument is, in fact, a heavily disguised telescope. More precisely, it is a zenith telescope, pointing (obviously) straight up at the sky and the zenith, which is the point in the celestial sphere directly above it. The inner edge of the spiral staircase leading up to the top of Monument (from which one can enjoy spectacular views of the city) forms the central shaft of the telescope, with the lenses in an opening in the golden urn at the top and the bottom. The shaft continues down into a small underground room, from which observations of the night sky could be made and scientific instruments stored.

The same type of telescope was used by the NASA Orbital Debris Observatory in New Mexico to detect the junk we’ve left careering through space. It was dismantled in 2002, but its parts now form part of the Large Zenith Telescope near Vancouver, third-largest optical telescope in North America. On the other hand, Hooke, having obtained funding in this very elaborate way, wanted to use his new telescope to measure tiny shifts in the position of the stars directly overhead and, using these measurements, calculate the radius of the Earth’s orbit around the Sun. Ultimately, though, it was only in 1838 that stellar parallax was measured for the first time, by Friedrich Bessel (of Bessel function fame, although actually discovered by Daniel Bernouilli) at the Königsberg Observatory.

Sadly, vibrations from the passing 43 bus to Friern Barnet (then a horse-drawn coach), as well as slight movements due to the wind, meant that Monument wasn’t an accurate enough telescope. In 1676, astronomical observations moved to the newly-built Royal Observatory in Greenwich, also partly based on Hooke’s design, leaving Monument to merely commemorate a careless baker and the most famous oven in history.

[Pictures. Banner: The Great Fire of London, Philippe–Jacques de Loutherbourg (1740–1812); Monument: copyright the author; Monument’s stairs: Nick Garrod, CC BY-NC-ND 2.0]