. The microscope and its revelations. ni-tion when measuring with apochromatic objectives than either theHuyghenian or Ramsden forms. (2) Different-powered eye-pieces can be employed. (3) By means of the screw which moves the micrometer websacross the field it is possible to perform measurements with the \\ebsequidistant from the centre of the field, and thus eliminate errorsdue to distortion. (4) The preceding advantage is secured without sacrificing thebenefit of a fixed zero web. Messrs. Zeiss have since adapted the compensating eye-piece totheir best screw micrometer. To use the scren- ni/
. The microscope and its revelations. ni-tion when measuring with apochromatic objectives than either theHuyghenian or Ramsden forms. (2) Different-powered eye-pieces can be employed. (3) By means of the screw which moves the micrometer websacross the field it is possible to perform measurements with the \\ebsequidistant from the centre of the field, and thus eliminate errorsdue to distortion. (4) The preceding advantage is secured without sacrificing thebenefit of a fixed zero web. Messrs. Zeiss have since adapted the compensating eye-piece totheir best screw micrometer. To use the scren- ni/rinniiti /• n-itli siiccess it should not be inserted,as the custom has been, like an ordinary eye-piece into the tube ofthe microscope, but It shoidd JMV& a Jinn stand quite independently,preventing actual contact with the body-tube. Plate II. gives the mode of its employment, the illustration beingmade from a photograph by Mr. Nelson. The micrometer eye-piece,it will be seen, is fitted into a stand wholly independent of the T. FIG. 214.—Nelsons new form of screwmicrometer eye-piece. 274 ACCESSORY APPARATUS microscope. This consists of a strong upright, fitted into a massivetripod 01- circnLir foot. The foot in either case only rests on threeI mints ; the upright is capable of telescopic extension by a clampingtube ; a short tube which takes the eye-piece is fixed to this uprightliv .1 compass joint. To use it. the object to be measured is placed in position, andthe microscope inclined in the usual way. The ordinary eye-pieceis removed, and the separate stand with the micrometer in its placeis put in front of the microscope, the extension tube being raised orlowered until the tube at the top of it, carrying the micrometer, ismade continuous with the tube of the microscope, as seen in thedrawing. It is well to leave from ^th to -j^ths of an inch of spacebetween the body-tube and the micrometer tube. It will be nowneedful to employ corrections to compensate for the increased
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
