In mid-October 2021 an image of the geoid based on data from NASA’s GRACE satellite was posted on LinkedIn. It was an object lesson in the perils of attempting to disseminate science via a platform that restricts posts to 2500 characters and comments to 1250 characters.
One milligal is approximately one millionth of the Earth’s gravity field, so it would seem that the periods of pendulums used for measuring gravity would have to be measured to a few millionths of a second for the results to be useful. This was simply not possible in the early nineteenth century, but pendulums were being used then to obtain results accurate to a few tens of milligal. How was it done?
Between April 1791 and January 1794, officers of Alejandro Malaspina’s mission to the Pacific measured gravity at no fewer than 17 different locations. It was the first truly global gravity survey, but how accurate was it?
In the past, we learned from people we respected how to do refraction surveys. Now we have committees to tell us what to do.
Peer review comes in for a lot of criticism, and University College London is trialling a different system. But historical precedents, going back to the early days of the Royal Society, suggest that it is unlikely to work.
A recent paper by Brandon Shuck and colleagues has presented detailed information from seismic reflection lines in the vicinity of the northernmost segment of the Macquarie Ridge Complex. For the regional picture, gravity maps are hard to beat, but they must be used with care.