Monthly microscopical journal: transactions of the Royal Microscopical Society, and record of histological research at home and abroad . hich are nowexposed by denudation and within the reach of our hammers. ( IHi ) IV.—On the Aperture of Object-glasses. By F. H, Wenham. The number of degrees that include a pencil of light radiatingfrom one single point from the focus of a microscope object-glass,represents the true angle of aperture. In order to obtain accurate results, the light indicating theadmitted degrees should be confined to a mere point or line situatedin that focus. In the diagram th
Monthly microscopical journal: transactions of the Royal Microscopical Society, and record of histological research at home and abroad . hich are nowexposed by denudation and within the reach of our hammers. ( IHi ) IV.—On the Aperture of Object-glasses. By F. H, Wenham. The number of degrees that include a pencil of light radiatingfrom one single point from the focus of a microscope object-glass,represents the true angle of aperture. In order to obtain accurate results, the light indicating theadmitted degrees should be confined to a mere point or line situatedin that focus. In the diagram the angles are the result of ascertained dimensionsfrom a kno^vn immersion object-glass, as follows :—Acting diameterof front lens, • 033 ; focal distance from the front surface, * 025,?with a width of field of • 020, or ijj inch. With correction adjusted^the resulting angle from central focal point is 66i-^, each ray givinga distinct image. In order to determine the direction of the outerrays by the usual sector method, a narrow slit must be set in the focus:the extreme light of the true aperture will pass through from Let the slit now be opened out to ^^ of an inch, so as to admitthe eflective obhque pencils embracing the entire field of will then enter from direction h. This ray will also show adistinct image, and an aperture of 93^ will now be indicated instead Oil Zeiss -isth Immersion. By W. J. Hickie. 185 of the former 664^. This excess of angle is a false quantity,because it does not come as a radiant from one single position in theaxial focal point, but from other lateral rays of the marginal foci. From this it may be inferred that unless precautions have beentaken to exclude these lateral pencils, all measurements for ascer-taining large apertures have hitherto been erroneous, and far inexcess of the true pencil from a single radiant point; and this sourceof error will exist from the same cause, whether the measurementis taken by means of the usua
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Keywords: ., bookcentury1800, bookdecade1860, bookpubli, booksubjectmicroscopy
