. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. 766 COMPOUND MICROSCOPE. in the compound microscope enables us to use an object-glass of a lower power than would otherwise be necessary. The compound microscope, when well constructed, gives a flat and colourless picture of the object, with clearness of definition. The observer can use it for a length of time with less fatigue than when employing the simple microscope. Weak eye-pieces and strong object-glasses are to be re- commended. The eye-piece does not add either
. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. 766 COMPOUND MICROSCOPE. in the compound microscope enables us to use an object-glass of a lower power than would otherwise be necessary. The compound microscope, when well constructed, gives a flat and colourless picture of the object, with clearness of definition. The observer can use it for a length of time with less fatigue than when employing the simple microscope. Weak eye-pieces and strong object-glasses are to be re- commended. The eye-piece does not add either clearness or distinctness to the object, and when it is very powerful the field of view becomes too small to take in the whole image formed by the object-glass; for the magnitude of the field of view and the strength of the iUuminar tion diminishes according to the magnifying power of the eye-piece employed. The lower powers are of use in searching for the object to be examined, which may thus be more easily found by a higher power. For the lower power a linear amplification of from 20 to 50 diameters, and for a higher power a linear amplification of from 300 to 500 diameters at most, will give a sufficiently wide range of powers. The powers are increased by a more powerful eye- piece or object-glass, or by both, or by lengthening the tube of the microscope. In examining vegetable structures, an instrument magnifying 150 to 200 diameters is usually suffi- cient ; but in some instan- ces higher powers are re- quired. Achromatic object- lenses of 1^, -I, and \ of an inch focal length are recom- mended as the most essen- tial ; and two eye-pieces should be provided, one of about 1^ and the other of 21 inches in length. The instrument shoidd have both a coarse and a fine adjustment; and it is of importance that it should be made to incline or to stand vertical. A movable stage is also useful, and a spring-holder to fix the objects on the stage, so that the different parts of the o
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectbotany, bookyear1875
