nd consequently the beam of re- In Professor Balestrieri's apparatus the focal point is ar- flected light will be composed of parallel rays. bitrary, and the segments can be adjusted to suit it at any Fig. 4 represents a section of an assemblage of these re- position, to give, say, a focal distance… … For lighthouses, at the present time the Fresnel lens is set of segments, or at most two, would replace the dozen parts, 1, 2, 3, 1', 2', 3', etc. Take any point on the line, A B, largely employed; but this is subject to the disadvantages lenticular systems, besides affording a greater simplicity…
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