. Light, a textbook for students who have had one year of physics. e telescope.—44. Magnifying power.—45. Ramsden eyepiece.—46. Opera glass.—47. Prism binocular.—48. Reflecting telescopes.—49. Simple microscope.—50. Compound microscope.—51. Projection lan-terns. 43. The telescope.—The essential part of a telescope istwo lenses,—a long-focus, large diameter achromatic, turnedtoward the object in view and therefore known as the objective,and a smaller lens (or, as we shall see later, more commonlya pair of lenses) called the eyepiece. Figure 54 shoAvs a sim-ple diagram of a telescope. The object
. Light, a textbook for students who have had one year of physics. e telescope.—44. Magnifying power.—45. Ramsden eyepiece.—46. Opera glass.—47. Prism binocular.—48. Reflecting telescopes.—49. Simple microscope.—50. Compound microscope.—51. Projection lan-terns. 43. The telescope.—The essential part of a telescope istwo lenses,—a long-focus, large diameter achromatic, turnedtoward the object in view and therefore known as the objective,and a smaller lens (or, as we shall see later, more commonlya pair of lenses) called the eyepiece. Figure 54 shoAvs a sim-ple diagram of a telescope. The object viewed is supposed to bean arrow, very far away, but so large that in spite of distanceit covers an angle of a degree or so. If this conception seemstoo artificial, we may think of the point of the arrow as repre-senting one star, the butt another. Wavefronts are not indi-cated, but lines are drawn to show the course, through the in-strument, of the cone of light from each end of the lines show the undeviated rays for each A real inverted image of the object is formed in the focalplane of the objective, from which the waves continue on,diverging from this image exactly as if it were a materialobject, except that the light is limited to a comparatively smallcone. This light falls upon the eyepiece, which forms with ita second image, really an image of an image. Since the raysthat form any point of the first image are limited to the conethat comes through the objective, it may well happen that theundeviated ray drawn from this point through the center ofthe eyepiece lies outside the cone and therefore does not existas a real ray. But the position of the second image must cer- (97) 98 LIGHT tainly be independent of the diameter of the objective, andtherefore we are at liberty in such a ease to find that positionby drawing fictitious undeviated rays just as if they reallydid exist. The figure is drawn for such a case. The positionof the seco
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectlight, bookyear1921
