An introduction to the study of the Diatomaceae . onnecting the top of the illuminatorwith the bottom of the slide under observation with a dropof oil. For general work Watsons Achromatic Condenser of1 is the most useful, as not only can it be successfullyemployed with lenses of large aperture, but by removing thetop lens is suitable for medium powers. For the mostcritical work with the largest angled apochromaticobjectives, Powell and Lealands apochromatic immersioncondenser of 1*4 is superior to anything that hasyet been produced. The most useful eyepiece to employ is a compensatin
An introduction to the study of the Diatomaceae . onnecting the top of the illuminatorwith the bottom of the slide under observation with a dropof oil. For general work Watsons Achromatic Condenser of1 is the most useful, as not only can it be successfullyemployed with lenses of large aperture, but by removing thetop lens is suitable for medium powers. For the mostcritical work with the largest angled apochromaticobjectives, Powell and Lealands apochromatic immersioncondenser of 1*4 is superior to anything that hasyet been produced. The most useful eyepiece to employ is a compensating one,magnifying about 10 or 12 diameters. The above-mentionedappliances will complete the dsciderata to enable the studentto carefully examine his specimens during the day time. Ifwork is to be done in the evening a lamp should be lamp will answer the purpose, but a microscope lampis preferable as it enables the observer to turn the edge of the 56 AN INTRODUCTION TO THE flame towards the mirror. Fig. 3 shows the lamp used bythe FIG. 3. The condenser should be racked up and down until theedge of the flame is sharply focussed upon the object andby this means a critical image may be obtained. If the objective is flooded with light a diaphragm shouldbe placed under the condenser to reduce the angle of thecone of light entering the objective. Should this cone betoo much reduced in angle a double outline will surround theDiatom. Living specimens should be examined in a live-box, whentheir movements may be observed, and their velocity com-puted by the aid of an eye-piece micrometer, and a stop STUDY OF THE DIATOMACE^E. 57 watch. When making such examinations it is instructive toadd granules of carmine (from a cake of water-colour) with acamel-hair pencil to the water containing the will be seen to follow such currents as are made bythe moving Diatoms, and in many instances to becomeattached to the gelatinous envelope, especially along theraphe of such
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Keywords: ., bo, bookcentury1800, bookdecade1890, bookidintroductiontost00mill
