. Lighthouse construction and illumination; . allic reflection is employed, but becausetwo agents are needed for all but the central portion of therays, thus causing a large loss, to which Fresnel himself wasfully alive, as appears from this passage in his Memoire of1822 (p. 17):—Mais comme on est oblig^ demployer desglaces etamees pour ramener dans une direction horizontaleles faisceaux lumineux qui sortent de ces lentilles, une grandepartie de la lumiere incidente est absorbee j)ar les miroirs,malgre leur iuclinaison prononcee, qui est de 25°; et jdstimeque la lumiere incidente doit itre rSd
. Lighthouse construction and illumination; . allic reflection is employed, but becausetwo agents are needed for all but the central portion of therays, thus causing a large loss, to which Fresnel himself wasfully alive, as appears from this passage in his Memoire of1822 (p. 17):—Mais comme on est oblig^ demployer desglaces etamees pour ramener dans une direction horizontaleles faisceaux lumineux qui sortent de ces lentilles, une grandepartie de la lumiere incidente est absorbee j)ar les miroirs,malgre leur iuclinaison prononcee, qui est de 25°; et jdstimeque la lumiere incidente doit itre rSduite ct vioitid ^mr son2oassage cm travers des lentilles et sa reflexion sur ces glacesUanUes! The first light on this principle was that ofCordouan in 1822. 18. FresneVs Fixed Light, varied ly Flashes. — Thisdistinction (Figs. 41 and 42), Fresnel produced by placingliis straight refracting prisms r (13, 4) on a revolving frame outside of his fixed lightapparatus p x. Now, as thatapparatus paralleKses the raysin the vertical plane
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Keywords: ., bookcentury1800, bookdecade1880, bookpublisherlondo, bookyear1881
