I think Alistair might have mangled the story there. There does seem to be a Charles II/fish/weight story, but about a completely different weight—in water, not postmortem: https://gwern.net/doc/philosophy/epistemology/1948-oesper.pdf Fortunately, while the question Charles II posed in this version is considerably clunkier, the upshot remains the same, so there are much worse leprechauns...
(Although the sourcing here is still thinner than I’d like and may not be the original: no date is given, but Schönbein was born in 1799 and Charles II died in 1685, and an 1842 publication still leaves at least 157 years between the latest the story could’ve happened and this exact publication. But I’ll leave it to someone else to try to track it further back.)
I think Alistair might have mangled the story there. There does seem to be a Charles II/fish/weight story, but about a completely different weight—in water, not postmortem: https://gwern.net/doc/philosophy/epistemology/1948-oesper.pdf Fortunately, while the question Charles II posed in this version is considerably clunkier, the upshot remains the same, so there are much worse leprechauns...
(Although the sourcing here is still thinner than I’d like and may not be the original: no date is given, but Schönbein was born in 1799 and Charles II died in 1685, and an 1842 publication still leaves at least 157 years between the latest the story could’ve happened and this exact publication. But I’ll leave it to someone else to try to track it further back.)