Lectures on light, delivered in the United States in 1872-'73; with an appendix (1873)
Tyndall, John, 1820-1893 · New York, Appleton · leaf 137
e to a certainextent diffused. We place a convex lens in the pathof the beam; the light is converged to a focus, and atthat focus you see that paper is not only pierced and aburning ring formed, but that it is instantly set ablaze.Many metals may be burned up in the same way. Inour first lecture… … the concave mirror, L the lens, at the focus C of whichcombustion is effected.) Dr. Scoresby succeeded in ex- ASSOCIATION OF HEAT AND LIGHT. 133 ploding gunpowder by the suns rays converged bylarge lenses of ice; the same effect may be producedwith a small lens, and with a terrestrial source of…
Optics
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