Last Friday saw 1,500 people of all ages congregating under a fabulous mix of lights, music, research, and dinosaurs. The event, ‘Lost Late’, formed part of the national Being Human festival, hosted by both the Natural History and Pitt Rivers museums in Oxford. From 7pm until the early hours of the morning (10pm) visitors could stroll through the two connected museums, which had been utterly transformed into a realm of discovery, from mazes to archaeological dig sites.

It was a terrific opportunity to engage people of all backgrounds and walks of life with research, which so often feels starkly detached from the rest of our society. I could be found in a dimly-lit room, demonstrating 3 optics experiments – each one representing a progressive stepping stone in medieval understandings of light, refraction, and rainbows. From the refraction instrument of Ptolemy, later used by Alhazen and then Witello; to Grosseteste’s conical model of rainbow formation; finally arriving at Theodoric of Freiberg and Kamal al-Farisi’s correct model of the rainbow as formed from a transparent sphere. The aim was to take visitors on a journey through time and scientific discovery.

For many centuries, scientific discourse on the rainbow was dominated by Aristotle’s contribution, who sought to explain its optics solely with reflection. It was only after increasing theoretical and experimental curiosity about refraction and its possibilities, that Grosseteste gave the field an about-turn in the 13th century. As we discuss in our paper, Bow-shaped caustics from conical prisms: a 13th-century account of rainbow formation from Robert Grosseteste’s De iride”, his theory was the first to try to explain rainbow optics with refraction, which unlike reflection, can indeed give rise to colourful spectrum-like projections.

In this demonstration, Grosseteste’s cone presented something of a ‘missing link’ in the evolution of optics from classical to modern times. Although once dismissed by historians of science as nonsensical and unintelligible, when his treatise De iride [On the Rainbow] was given a thorough analysis by an interdisciplinary team, we discovered something very exciting. Far from being unable to account for any optical phenomenon (as said by Lindberg in Theorise of Vision), his rainbow scheme does correctly describe the optical projections of light through a transparent cone, which results in a dazzling display of a brightly coloured bow.

Over the course of the evening, well over 100 visitors came to the medieval optics room to see the experiments, as well as participating themselves using torches and laser pens (a historically inaccurate stand-in for acamera obscura!) to make rainbows and measure angles of refraction. Bringing along their curiosity, questions, experiences and enthusiasm, engaging the public with research is always a rewarding experience, reminding us that research does not have to be a reclusive, isolating process. Rather, it is creative connection – between ideas, disciplines, and communities – that is the engine that drives research.

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