. The microscope and its revelations. should be a notch in the slot or arm which carries thebulls-eye to denote when the flame of the lamp is in its principalfocus. The above are fundamental principles of illumination, and if thestudent is to succeed as a manipulator he must demonstrate and re-demonstrate them, and become master of their details and what theycollaterally teach. We may, however, with much advantage give them a larger andmore detailed application to the practical setting up of a dark-ground illumination, as in fig. 356. Let an object such as a triceratnnn (diatom) be taken, and
. The microscope and its revelations. should be a notch in the slot or arm which carries thebulls-eye to denote when the flame of the lamp is in its principalfocus. The above are fundamental principles of illumination, and if thestudent is to succeed as a manipulator he must demonstrate and re-demonstrate them, and become master of their details and what theycollaterally teach. We may, however, with much advantage give them a larger andmore detailed application to the practical setting up of a dark-ground illumination, as in fig. 356. Let an object such as a triceratnnn (diatom) be taken, and sup-pose that the objective employed is a §-inch of -2H We mustfirst adjust the lamp and bulls-eye, as in fig. 344. and get the edgeof the lamp flame extended to a disc as at A. Now let a small aperture be put into the conden>er and a tri-ceralium on the stage and the § objective on the nose-piece. The microscope being put into position, the lamp should beplaced on the left-hand side of it—a lamp with a fixed bulls-eye is. FIG. 3(50. FIG. 301. FIG. 362, FIG. 363. assumed—and it should now be arranged as to height, so that therays from the bulls-eye should fall fairly on the plane mirror, thislatter being inclined so as to reflect the beam on the back of thesub-stage condenser. Xow, with any kind of light, focus, and place in the centre of thefield, the triceratium, as in fig. 360 ; then rack the condenser untilthe small aperture in its diaphragm comes into focus ; centre thisto the triceratium, as in fig. 361. Rack the condenser closer upuntil the bulls-eye is in focus, as in fig. 362. Here it happens that the bulls-eye is not in the centre, and it isnot uniformly filled with lif/ht, but has instead two crescents of light. This is a case which frequently repeats itself, but it is of coursenot inevitable. The bulls-eye may be more or tilled with may or may not be more nearly centred. In this case \\e havenext to centre the image of the bulls-eye to
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
