Burning glass, mid-18th century
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  Photo courtesy of Atwater Kent Museum of Philadelphia |
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England
Crystal and leather; L. 4 1/2 in. (11.4 cm), W. 2 5/8 in. (6.7 cm), D. 3/8 in. (1.0 cm) Atwater Kent Museum of Philadelphia, The Historical Society of Pennsylvania Collection (Philadelphia, Pa.), HSP.C.1.7 
This "burning glass" is a convex lens that will concentrate the beams of light, and raise the temperature of an object beneath it until it bursts into flame.
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