Six lectures on light : delivered in America in 1872-1878 (1886)
Tyndall, John, 1820-1893 · New York : D. Appleton · leaf 200
more and more concentrated, until finallythey are able to pierce black paper with a burning ring.Pushing back the lens so as to render the rays paralleland receiving them upon a concave mirror, they arebrought to a focus; paper placed at that focus is causedto smoke and burn. Heat of this intensity… … placed a lamp, in all particulars similar to those alreadyemployed. But instead of gathering up the rays fromthe carbon-points by a condensing lens, we gatlier themup by a concave mirror {m m/, fig 50), silvered in frontand placed behind the carbons (P). By this mirror wecan cause the rays to issue…
Light
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