Gravity for Geologists

Abstract

When I was quite a small boy I was fully prepared to believe that the world was round, if older people said so ; but I refused to believe that I was ever on the underneath side of it. Like most of you when you also were young, I had swung upside down from the branches of trees and the cross-bar, and could stand on my head, provided that there was a wall behind against which I could put my feet when I felt wobbly: so I knew what it felt like to be upside down, and refused to believe that either I or people in England (and it must be one or the other) walked about upside down on the spherical earth. Later on I knew it must be true, but was not in the least helped by being told that none of us were upside down, because there wasn't any such thing as up and down; that the sky was always " up ", and as long as I kept the sky above my head I was right side up, but that when I put my head nearer the ground and my feet up towards the sky, I was officially "upside down ". What difference could it make whether I tipped upside down from a cross-bar, or walked round to the other side of the world, or let the earth revolve and tip me upside down! In any case, I would now be presenting my feet to the patch of sky that previously had admired the top of my head.