Aravind: Sunsets, Tall Buildings and the Earth's Radius

Padmanabhan Krishna Aravind (No.501)

Mayo College, 1964-67.

I have written a paper entitled Sunsets, tall buildings, and the Earth's radius  as a tribute to Gibson's memory and posted it on the e-print archive. In this paper I show how one can use a tall building to determine the Earth's radius. The idea is to go up the building and observe sunset repeatedly from a number of different floors, and then use the heights of the floors and the times of the sunsets to infer the Earth's radius. The experiment tries to bring together a number of things Mr.Gibson liked: Eratosthenes, geometry, great heights (although a tall building is a poor substitute for a mountain!) and a combination of physical and mental activity directed towards a useful end. I don't know how Gibson would have reacted to the experiment I propose, but of one thing I am certain: if he had decided to carry it out himself, he would have disdained the elevators and dashed up the stairs, with a band of schoolboys in tow.