. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. tiful iris diaphragm of Messrs. Beck (Fig. 27), both of which allow the aperture under the stage to be gradually diminished or enlarged without the interval Fig. of darkness which occurs during the shifting of theordinary wheel of diaphragms. A very useful illumination, resembling the light ofa white cloud, may be obtained by placing a pieceof white paper over the mirror, and concentratingthe light of a lamp upon it by means of the con-de
. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. tiful iris diaphragm of Messrs. Beck (Fig. 27), both of which allow the aperture under the stage to be gradually diminished or enlarged without the interval Fig. of darkness which occurs during the shifting of theordinary wheel of diaphragms. A very useful illumination, resembling the light ofa white cloud, may be obtained by placing a pieceof white paper over the mirror, and concentratingthe light of a lamp upon it by means of the con-densing lens. The soft white light so producedis extremely pleasant to use, and suits delicate and DARK FIELD ILLUMINATION. 107 transparent obje(5ls viewed with the binocular, andwill be found of more general service than the fulllight of the mirror, which, with the double body,often produces a most disagreeable glare, which onlyobscures and confuses instead of defining. The mirror affords the simplest means of obtainingwhat is known as dark field illumination, for whichwe are indebted to the Rev. J. B. Reade, ,President of the Royal Microscopical Society. Hisoriginal contrivance consisted of an ordinary con-densing lens, so placed with respedt to the lamp andthe stage, that it transmitted a pencil of such
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectmicroscopy, bookyear1
