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:
“The burning of rebellious thoughts in the little breast, of internal hatred and opposition, could not long go on without slight whiffs of external smoke, such as mark the course of subterranean fire.”
—Harriet Beecher Stowe (1811–1896)
“... this I conceive to be no time to prate of moral influences. Our men’s nerves require their accustomed narcotics and a glass of whiskey is a powerful friend in a sunstroke, and these poor fellows fall senseless on their heavy drills.”
—Clara Barton (1821–1912)