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:
“He certainly must be a son of Aurora to whom the sun looms, when there are so many millions to whom it glooms rather, or who will never see it till an hour after it has risen. But it behooves us old stagers to keep our lamps trimmed and burning to the last, and not trust to the sun’s looming.”
—Henry David Thoreau (1817–1862)
“It is difficult to read. The page is dark.
Yet he knows what it is that he expects.
The page is blank or a frame without a glass
Or a glass that is empty when he looks.”
—Wallace Stevens (1879–1955)