. Annals of the Andersonian Naturalists' Society. THE ILLUMINATION OF MICROSCOPIC OBJECTS. By J. R. Jack, (Read loth September, igi2.) Although most naturalists make considerable use of the microscope comparatively few obtain the best results which are possible. Considerable care is spent in focussing the instrument upon the object, but the observer is frequently puzzled to know why the same object can be seen very much better on some occasions than on others. In most cases this is due to variations in the illumination, and to obtain what is known as a "critical" image it is
. Annals of the Andersonian Naturalists' Society. THE ILLUMINATION OF MICROSCOPIC OBJECTS. By J. R. Jack, (Read loth September, igi2.) Although most naturalists make considerable use of the microscope comparatively few obtain the best results which are possible. Considerable care is spent in focussing the instrument upon the object, but the observer is frequently puzzled to know why the same object can be seen very much better on some occasions than on others. In most cases this is due to variations in the illumination, and to obtain what is known as a "critical" image it is necessary to take as much care with the optical system on the condenser side as with that on the objective side. This may easily be seen by considering the principles underlying microscopic pro- jection. In fig. 1, let O be the object and L the object Fis- 1 From every point in 0 rays diverge, some of which fall upon the object glass L, which brings them to a focus at the corresponding or "anti point" in the image. This image may either be received on a sensitive plate or may be further enlarged by means of an eye-piece. Since the image is formed only by rays which have followed such paths it is evident that no other light is of any value in forming the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Andersonian Naturalists' Society. Glasgow
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Keywords: ., 1908, bookcentury1900, bookdecade1900, bookpublisherglasgow, booky
