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 host is rushing ‘twixt night and day,
And where is there hope or deed as fair?
Caoilte tossing his burning hair,
And Niamh calling Away, come away.”
—William Butler Yeats (1865–1939)
“People who, out of an inborn moderation, leave every glass standing only half-emptied refuse to admit that everything in the world has its sediments and dregs.”
—Friedrich Nietzsche (1844–1900)