Refractive sundial, 1578
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  Photo courtesy of American Philosophical Society |
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Augsburg, Germany
Christopher Schissler Copper, brass, silver, and gilding; Diam. 12 in. (30.5 cm) American Philosophical Society (Philadelphia, Pa.), 58-66 
Comparison between this implement and Franklin's electrostatic machine illustrates vividly the advances in the study of the physical sciences during the years from its creation to Franklin's period of experimentation.
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