23/52 The two forms of eye-piece most commonly employed are exhibited in figs. 5 and 6.Fig.5 is Huyghens' eye-piece, called also the _negative_ eye-piece, because a real image is formed _behind_ the _field-glass_ (the lens which lies nearest to the object-glass). Fig. 6 represents Ramsden's eye-piece, called also the _positive_ eye-piece, because the real image formed by the object-glass lies _in front of_ the field-glass. |