What metaphors are used in Science and the Enlightenment by Thomas L. Hankins?

Hankins does not employ metaphor in the text. He does, however, note Volta's experiments with the Leyden jar and his stacks of cakes showed that the atmosphere and fluids theories must be mistaken. Volta created a crude battery out of materials lying around his laboratory to generate an electric charge that was not depleted. This result showed that electricity could not be either an atmosphere of two fluids because either one of these things would be depleted eventually; whereas, Volta's charge was not depleted. A related experiment by Galvani involving frog legs hinted at something further. He found that a dissected frog leg would kick in the presence of electricity. This device, the frog leg, was the most sensitive detector of electricity available at the time and allowed for more minute measurements. Volta, experimenting further, created a constant electrical current out of his crude battery. After these experiments, electricity was metaphorically still thought of as a fluid, though the actual mechanical "subtle fluids" theory was dropped.