The microscope : and its application to vegetable anatomy and physiology / by Dr. Hermann Schacht ; edited by Frederick Currey, M. A.

  • Hermann Schacht
Date:
1855
Catalogue details

Licence: Public Domain Mark

Credit: The microscope : and its application to vegetable anatomy and physiology / by Dr. Hermann Schacht ; edited by Frederick Currey, M. A. Source: Wellcome Collection.

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    moved up and down by means of the action of the large milled head seen in the figm-e, and of a con-esponding milled head on the opposite side. In all the best microscopes there is an ad- ditional apparatus for adjustment, called the Jim adjustment, by which the object-ghiss may be brought very gradually nearer or further from the object. This is indispensable when high j>oWei’S are eni})loyed. It is effected by a screw with a fine milled head, and is seen in the Frontisjiiece in front, and in fig. 20 behind the coni])ound body. The manner in which the screw acts varies in diftei'ent instruments. In some it has a conical point, wliich presses against a sht in an inner tube; in others it acts by means of a lever. OPTICAL PARTS. These consist, as has been stated, of the miiTor, the object- glasses, and the eye-pieees. Tii« miirror.—The miiTor, as will be seen by reference to the Frontisiiiece and to fig. 20, is circular. It has two silvered glasses, one concave and the other plane. The effect of the concave side is to cause the rays of light to converge, whilst the plane mii-ror reflects them parallel to one another. The mirror is eapable of being moved by joints in every direction, and should be made so as to slide uji and down the bar, in order that the rays from the concave surface may, if necessary, be brought to a focus upon any object on the stage, Tiie Object-glasses.—The construction of a modern achro- matic object-glass is shewn in section in fig. 22. A.U object-glass, such as is there represented, con- sists of three })lano-convex lenses with the plane side towards the object; each lens is, in fact, com- pound, consisting of a double convex lens cement- ed to a plano-concave one, the two component lenses being made of glass of difierent densities. The manner in which such a glass acts in form- ing an image is as follows:—The object is })laced within the jirincijial focus of the anterior lens, so that a 'sdi’tual image is formed in front of the lens ; the rays from this image tall on the second lens, but the image is so near, even to the second lens, as to cause the formation of a second virtual Fig. 22.