Gravity in the Nordic Area from Newton till Today:
What, how, and why?

Martin Ekman

Summer Institute for Historical Geophysics, Åland Islands, 2024
ISBN 978-952-94-9218-3
Hard cover, 113 pages, 8 tables, 38 figures

Description of the book (from its back cover)

This is a book about the Earth’s gravity, about what it is, how it has been determined, and why it has been useful to know it. The book has a historical perspective, spanning three centuries, and a northern perspective, dealing mainly with the Nordic area.

The historical perspective of three centuries is quite natural, since it all started with the ideas of Newton a little more than 300 years ago. The Nordic perspective has several reasons: First, early gravity measurements with pendulums were made as far north as possible to try to verify Newton’s prediction of a flattening of the Earth at its poles, and to determine the value of the flattening. Second, Nordic scientists later invented spring gravimeters facilitating gravity measurements to search for minerals, and started studying inner parts of the Earth. Third, gravity measurements at sea and on the ice cover of the sea were performed early in the Arctic and the Baltic Seas. Fourth, the postglacial rebound of the Nordic area has been investigated by repeated gravity measurements, lately also involving fall instruments. Fifth, the recently started melting of the Greenland ice sheet due to the ongoing climate warming has been revealed by repeated gravity measurements, in this case using satellites. Finally, the outlook at the end of the book, dealing with Einstein’s view on the subject, also has a Nordic flavour, involving interesting problems with his Nobel prize.

The book is intended not only for gravity people, but for a wider audience with an interest in the constitution and the changes of the Earth, or with an interest in the historical development in Earth sciences.

Table of contents

1. Preface
2. Background: What is gravity? Newton and his idea
3. Gravity and latitude: The Earth’s flattening at the poles
   1. Trying to prove Newton’s theory at the Arctic Circle
   2. Is the Earth denser towards its centre?
   3. Shipping pendulums to the Arctic coasts
   4. The Earth’s flattening from more gravity data
4. Gravity and location: Crustal thickness, northern minerals and the geoid
   1. Early gravity networks and an experiment in the north
   2. Investigating the crust and below
   3. A Nordic novelty: Spring gravimeters
   4. Mineral exploration and geoid determination
   5. New gravity networks and a geophysical surprise
   6. A Baltic venture: Gravity on sea ice
   7. Gravity from fall and adherent gravity networks
5. Gravity and time: Postglacial rebound and mass flow
   1. Missing mass in the mantle?
   2. The Nordic land uplift gravity lines
   3. Repeated absolute gravity and land uplift
   4. Influence of Moon and Sun: Earth tides
   5. Smaller gravity changes
6. Gravity and satellites: The Earth from space and climate effects
   1. The Earth’s gravity field and perturbations of satellite orbits
   2. The Nordic geoid from satellite orbits and surface gravity
   3. Special gravity satellites and the Greenland ice sheet
   4. A brief review
7. Outlook: What is gravity? Einstein and the Nobel prize
8. Appendix A: Gravity determinations at the Uppsala Observatory during three centuries
9. Appendix B: Gravity and the size of large animals
10. References
11. Illustrations
12. Index