Maskelyne, the man who used a Munro to weigh the Earth

All students and staff welcome.

Speaker 

Prof Malcolm McMahon, Professor of High Pressure Physics, School of Physics and Astronomy, University of Edinburgh.

Maskelyne, the man who used a Munro to weigh the Earth

250 years ago, in the summer of 1774, Nevil Maskelyne, the Astronomer Royal, spend 3 months camped on the side of a Scottish mountain trying to measure its gravitational attraction on a pendulum. By making extremely accurate measurements of the positions of 142 stars, he was able to show that the sum of the deflections measured north and south of the mountain was 0.00322 degrees. A subsequent geographic survey of the mountain determined its dimensions and average density, and enabled him to determine the density of the Earth as 4.5 g/cc. This proved the Earth was solid, with a high-density core, and confirmed Newton’s law of gravitation.

In this talk I will describe the Maskelyne experiment – perhaps the most important physics experiment ever conducted in Scotland - and the results of a similar experiment conducted in 1856 using Arthur's Seat in Edinburgh. Finally, I will show how modern topographic data obtained from the space shuttle, combined with Maskelyne's measurements, can be combined to give a very accurate measurement of the earth's density, as well as a determination of the gravitational deflections induced by the great pyramids in Egypt.

Refreshments

Meet us at 16.30 outside the Elm lecture theatre in the Nucleus Building for tea and cakes prior to the talk.