. Quarterly journal of microscopical science . ly the part of a Leiberkuhn,with the advantage of more perfect reflection. A lens of this description may be let into a thin plate ofbi-ass as in fig. 2, and used in the same way as an aquaticholder, the parabolic condenser always being used for concen-trating the light. When a slide containing balsam-mountedobjects is placed above the lens, instead of using water, it ispreferable to employ turpentine, or oil of cloves ; the refractiveindex of the latter being nearly the same as crown glass. Thereason for introducing this agent is because light im
. Quarterly journal of microscopical science . ly the part of a Leiberkuhn,with the advantage of more perfect reflection. A lens of this description may be let into a thin plate ofbi-ass as in fig. 2, and used in the same way as an aquaticholder, the parabolic condenser always being used for concen-trating the light. When a slide containing balsam-mountedobjects is placed above the lens, instead of using water, it ispreferable to employ turpentine, or oil of cloves ; the refractiveindex of the latter being nearly the same as crown glass. Thereason for introducing this agent is because light impingingupon the polished plane between a greater and a less refractivemedium, will always suffer total reflection at the surface ofthe former, at a given angle dependent upon the relativerefrangibilities. If water is used, the angle of the illuminatingpencil will be limited to about 160°; above this, all rays willbe reflected down again by the flat surface of the lens, andlost, as shown by fig. 4; a a represents the glass slide, with Fig. 4,. objects in balsam ; 5 is a hemispherical lens placed underneaththe slide, with water interposed ; c c, rays which pass onwardsto the top plane of tlie tliin glass cover, to be reflected downagain upon the object: the dotted lines, dd, are the portionsof the illuminating pencil, that will be lost by being reflectedIrom the flat surface of the lots—of course if a medium ofnearly tlie same refractive power as the glass is used, such asoil of cloves, all this light will be transmitted and renderedavailable. Another variation in this principle of illuminatinLr opaqueobjects, is that illustrated by fig. 5 : « is a small paraboloid ofsolid glass with a flat top. A black stop, /;, of the samediameter as the apex, is fixed at the base of the parabola, for llhuninatiiitj Opaque Objects. 51) tlie j)urpose of stopping out direct rays. This paraboloid isset in a ring, which is screwed underneath a flat l)iass plate,
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Keywords: ., bookcentury1800, bookdecade1850, bookpublisheroxfor, bookyear1853
