Over a year ago I wrote a post ‘Sympathetic vibrations‘ that mentioned a 1688 pamphlet that included (as satire) a means of finding longitude by using a ‘Powder of Sympathy’. The idea was that this could be used to enduce an on-board dog to yelp at a pre-determined time at a known reference point, thus allowing a comparison with local time and, hence, a calculation of longitude. I noted there the fact that this story has often been presented as a genuine longitude scheme, probably because it is useful in getting across the basic point about time difference.
The other day I came across a genuine attempt to locate a longitudinal position that makes this time difference = longitude difference point just as forcefully. While it would today be discounted as pseudo-science, like the powder of sympathy, it relates to real events and a story that has a number of nice resonances with the History of the Board of Longitude project, despite being a few decades later: Arctic exploration, magnetism (or mesmerism), and longitude. [Read more]