There is something touchingly noble in this:
(p. 11) There is no direct evidence in the historical record, but it is entirely probable that it was the waterspout sighting that sent Priestley off on his quest to measure the temperature of the sea, trying to marshal supporting evidence for a passing conjecture his friend had made a decade before. Franklin had been dead for nearly four years, but their intellectual collaboration continued, undeterred by war, distance, even death.
Source:
Johnson, Steven. The Invention of Air: A Story of Science, Faith, Revolution, and the Birth of America. New York: Riverhead Books, 2008.