A burning glass or burning lens is a large convex lens that can concentrate the sun's rays onto a small area, heating up the area and thus resulting in ignition of the exposed surface. Burning mirrors achieve a similar effect by using reflecting surfaces to focus the light. They were used in 18th-century chemical studies for burning materials in closed glass vessels where the products of combustion could be trapped for analysis. The burning glass was a useful contrivance in the days before electrical ignition was easily achieved.
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Famous quotes containing the words burning and/or glass:
“Personal prudence, even when dictated by quite other than selfish considerations, surely is no special virtue in a military man; while an excessive love of glory, impassioning a less burning impulse, the honest sense of duty, is the first.”
—Herman Melville (1819–1891)
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