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Introducing engineering
Introducing engineering

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5.1.1 Luigi Galvani (1737–98)

Under these circumstances of curiosity, it is not surprising that Galvani, a physician by training, was studying the interaction of electricity with animals. Galvani had noticed that when a dead, partially dissected frog happened to come into the path of an electrical discharge, the leg muscles flexed, twitching the legs as though in a spasm. More curiously, sometimes the frog needed only to be near Galvani's electrical machine to be so affected, not necessarily directly in the path of a spark. Subsequently, it was realised that twitching accompanied nearby sparks when the spinal cord of the frog was pierced by a grounded metal (i.e. a piece of metal that was connected to the ground and so would act as a path for draining away charge). It can't have been long before Galvani was planning experiments with the ultimate spark, lightning – which, by the late 1740s, Benjamin Franklin had already shown to be electrical in nature. This was the chain of events that led to Galvani doing experiments that involved piercing the spinal cords of dissected frogs with metal hooks and hanging them from iron railings. The railings provided the effective path to ground. It is likely that the iron of the railings would have been scraped clean to ensure good electrical contact between the hook and the railing. The plan was presumably to set the specimens in place on a stormy day and to note any correlations between lightning flashes and twitching legs. The strange result was that some legs twitched as soon as they were hung on the railing – even in clear weather.