X-rated Bob wrote
PS: I still wish my musings about standards of proof to be considered. I have only a half-baked ideas myself about how vitamin C addresses scurvy or the causes of lightning (something to do with Thor brassoing his hammer)
One factor is effectiveness. The mechanism of vitamin C remained a mystery for many years after it's effect (or, more correctly, the effect of citrus fruits since they didn't know about vitamins) on scurvy was shown to have worked. Lime-eaters (hence, "Limies," for the English) - no scurvey. Non-lime-eaters - scurvey often. There were enough trials to show beyond reasonable doubt that there was a strong effect long before the mechanism was known.
Likewise with lightning, Franklin hypothesised certain things about lightning, conducted an experiment that bore it out (and famously nearly killed him). A few years after his discovery, his lightning rods were everywhere and it was clear to people that they worked as advertised. Strikes on other objects near lightning rods ceased. He imagined it had certain characteristics in common with electricity and designed experiments to test these ideas. The exact mechanism has still not been conclusively shown. But in the meantime, it is clear that his notions - and subsequent assumptions based on a theory of lightning as a natural, electrical phenomenon - work, while all previous ideas about lightning could not affect lightning strikes - which confusingly had a predilection for church steeples despite the popular idea that lightning strikes were punishment from God.
