The Encyclopedia britannica; a dictionary of arts, sciences, and general literatureWith new maps, and original American articles by eminent writersWith American revisions and additions, bringing each volume up to date . inches aperture already referred to ReJUettixg TtUxopt The folloning are the various forms of reflecting telescopes TheGregonao te is represented lo fig 12 A-4 and BB are v. T\Q 12 —Gregorian telescowconcave mirrors having a common axis and their concanties facingw each other The fcKus of A for parallel rays is at F that of B for I parallel rays at/—between B and F Parallel rav
The Encyclopedia britannica; a dictionary of arts, sciences, and general literatureWith new maps, and original American articles by eminent writersWith American revisions and additions, bringing each volume up to date . inches aperture already referred to ReJUettixg TtUxopt The folloning are the various forms of reflecting telescopes TheGregonao te is represented lo fig 12 A-4 and BB are v. T\Q 12 —Gregorian telescowconcave mirrors having a common axis and their concanties facingw each other The fcKus of A for parallel rays is at F that of B for I parallel rays at/—between B and F Parallel ravp falling on AA converge at F where an image is formed the rays are then re-flected from B and conTergeal P. where ase<ond and more enlargedimage w f*niied Gregory himself showpd that, if the large mirrorwere a segment of a paraboloid of revolntioo whose fo*us i? F andthe small mirror an ellipsoid of revolution whose f(vi are F and Prespectively, the resulting luia^e will I»e plane ana undistortedThe image formed at P i? viewed through the eye-piece at E whichmaybe of the Huygenian or Ramsd^^n typt The focal adjustment13 accomplished by the scrpw S. whirb acti on a slide carrying anarm to which the mirror B is aturhed The practical difBcuItyof coostnicting Gregorian telescopes ol eood nefining quality isvery considerable, b^ase ii spherical mirmrs are (employed theiraberrati
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Keywords: ., bookcentury1800, bookdecade1890, bookidencyclopedia, bookyear1892
