. The microscope and its revelations. S arc combined in the ; PARABOLIC ILLUMINATOR 317 parallel rays r r rf (fig. 259), entering its lower surface perpendicu-larly, pass on until they meet its parabolic surface, on which they fallat such an angle as to be totally reflected by it, and are all directedtowards its focus, F. The top of the paraboloid being ground out intoa spherical curve of which F is the centre, the rays in emerging fromit undergo no refraction, since each falls perpendicularly upon thepart of the surface through which it passes. A stop placed at Sprevents any of the rays
. The microscope and its revelations. S arc combined in the ; PARABOLIC ILLUMINATOR 317 parallel rays r r rf (fig. 259), entering its lower surface perpendicu-larly, pass on until they meet its parabolic surface, on which they fallat such an angle as to be totally reflected by it, and are all directedtowards its focus, F. The top of the paraboloid being ground out intoa spherical curve of which F is the centre, the rays in emerging fromit undergo no refraction, since each falls perpendicularly upon thepart of the surface through which it passes. A stop placed at Sprevents any of the rays reflected upwards by the mirror frompassing to the object, which, being placed at F, is illuminated bythe rays reflected into it from all sides of the paraboloid. Thoserays which pass through it diverge again at various .-ingles : and ifthe least of these, G F H, be greater than the angle of aperture ofthe object-glass, none of them can enter it. The stop 8 is attachedto a stem of wire, which passes vertically through the paraboloid.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
