8th Experimental Archaeology Conference abstract – James Bailie Russell
Measurement of Earth Circumference using only materials and techniques available to Neolithic peoples
James Bailie Russell
Member of the Institution of Engineers of Ireland, Graduate member of the Institution of Civil Engineers
This article has been written to explain one of two methods to establish the circumference of the earth, using a little understanding of how the Earth moves in space with respect to the Sun and stars, and only materials available to Megalithic People. Only five measurements need to be taken. The “vertical method” depends on the establishment of the elapsed time of stars passing through two vertical planes viewed towards the South from fixed eyepieces exactly North of two vertical rails at the same latitude a known distance apart. It is done at night to minimise optical distortion and thermal movements in the apparatus. If we know the distance between two points along this line and the time taken (seconds/pendulum swings) for a fixed point (Star) to pass directly overhead between the points, and we know the time for a full rotation (24 x 60 x 60 seconds), the circumference of the earth along the line of latitude is:
Circumference along line of latitude = (Distance between sightrails ∗ No of swings in 24 hours)/ No of swings between star overhead at each sightrail
Great Circle circumference = Earth Circumference at observer’s latitude/Cosine of Latitude
The unit of time for a modern experiment would be the second, a Neolithic experimenter could have used pendulum swings. A handheld pendulum should have an accuracy better than 15 minutes per day i.e. 1%.