Johnson's natural philosophy and key to philosophical charts : illustrated with 500 cuts; being reduced photographic copies of all the diagrams contained in the author's philosophical series of indestructible school charts ; for the use of schools and families (1878)
allow the instru-jiieiit to be reduced to a convenient length when not in use. ^91. Figure 24.—Herschels reflecting telescope.—There is a great variety of reflecting telescopes, in all of which a parabolic metallicspeculum or mirror (392) is employed, instead of the object-lens, to forman image of… … what less in diameter than the tube, with its axis directed to one sideof the tube, shown by the dotted line. The parallel rays, EF, fromsome very distant object, are received upon the mirror and reflected,converging, to the eye-piece, L. The size of the tube and the inclina-tion of the axis of the…
Physics · Astronomy
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