In this episode, Oliver takes through the ins and the outs of the Arago meridian line. The line was once France’s prime meridian, a line of longitude right through the centre of Paris, and essentially a semi-circle around the the world from north to south. It is from these lines that distance and time can be measured. France’s meridian was calculated in the 17th century, and developed more precisely by astronomer François Arago in the 19th century.