. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. remelysmall portions of space with great exaftness ; theinstrument, however, is rather expensive. With a view to avoid the multiplication of ap-paratus, the late George Jackson, by a simple con-trivance, rendered the ordinary Huyghenian eye-piece available for micrometric purposes. A slit wascut on each side just above the diaphragm (Fig. 43, A),which served to admit a brass slide, B, containing ascale ruled on glass, which, when in position,
. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. remelysmall portions of space with great exaftness ; theinstrument, however, is rather expensive. With a view to avoid the multiplication of ap-paratus, the late George Jackson, by a simple con-trivance, rendered the ordinary Huyghenian eye-piece available for micrometric purposes. A slit wascut on each side just above the diaphragm (Fig. 43, A),which served to admit a brass slide, B, containing ascale ruled on glass, which, when in position, was inthe focus of the eye-glass, and could be seen in thefield at the same time with the obje6t in the micro-scope. The scale is ruled with a long line at everyfifth division, and a still longer one at every tenth,for facility of reading. The scale is allowed a smallamount of lateral motion, which is controlled by afine screw adling against a spring on the opposite EYE-PIECE MICROMETER. 159 side. This movement enables the line from which the measurement commences to be brought to the edge of the objedl more accurately than it could be Fig. 43. A. b}^ means of the stage movements, as the scale ofthe eye-piece micrometer is only magnified by thetrifling power of the eye-glass, while the motion ofthe stage-racks is enlarged by the whole power of theinstrument. The operation of measuring is nearlyas-easy as applying an ordinary rule: the scale isbrought over the objecTt, adjusted by the screw, andthe number of degrees read off in the diredlionrequired. To determine the value of the degrees, whichdiffers with each objedtive, the following processmust be adopted :— Place the micrometer in its eye-piece, and focus, i6o MICROSCOPICAL MANIPULATION. if necessary, for distindt vision of the scale b} un-screwing the eye-glass, which is usually provided witha rather long screw for this purpo^. Screw on theobjedlive, and place the ruled scale on the stage; and,looking through the microsco
Size: 1797px × 1390px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectmicroscopy, bookyear1
