. The microscope; an introduction to microscopic methods and to histology. Microscopes. Ch. XII] HISTORY OF LENSES AND MICROSCOPES 435 h |;5 k P P 1 A ^!»= â ysN. for illuminating transparent objects for projection. The first pictures of compound microscopes with the mirror, as at present under the stage, are by Hertzel (1712) and Marshall (1718). A condenser of a single lens or of a combination of lenses for trans- parent objects dates from the earliest use of the compound microscope, as shown by Descartes' figure. Its importance for adequate fighting has never been lost sight of, as indicat
. The microscope; an introduction to microscopic methods and to histology. Microscopes. Ch. XII] HISTORY OF LENSES AND MICROSCOPES 435 h |;5 k P P 1 A ^!»= â ysN. for illuminating transparent objects for projection. The first pictures of compound microscopes with the mirror, as at present under the stage, are by Hertzel (1712) and Marshall (1718). A condenser of a single lens or of a combination of lenses for trans- parent objects dates from the earliest use of the compound microscope, as shown by Descartes' figure. Its importance for adequate fighting has never been lost sight of, as indicated by Brewster (§ looa) and by Nelson (see in coUateral reading); and never so thoroughly appreciated as at the present day. The form most common on microscopes is the uncorrected one of Abbe which was first described in the Archiv fiir Mikr. Anat. Vol. 9, 1873, p. 469. § 701. Achromatization. â As pointed out in § 463-464, white light, being composed of different wave lengths (fig. 144-146), must be differently refracted when passed through a prism or lens. To the normal human eye the different waves when separated or dispersed out into groups appear of different colors. Although the nomenclature used by Newton was somewhat different from that now used, he supposed that the refraction of the differ- ent waves was in exact accordance with their wave lengths, as is the case with a diffraction grating, and hence there could be no achro- matization of dioptric instruments, for when the dispersion was overcome the refraction must also be eliminated. The mistaken befief that the human eye was achromatic, however, kept afive the hope of producing achromatic microscopes and telescopes. Experiments on a large number of transparent substances showed that while all dispersed the light, the dispersion was not the same in all, some affecting one group out of proportion to another. This irregularity gave the clue to the way to. Fig. 252. Descartes' Simple Microscope. 11 Rays of
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