The microscope and its revelations . position, and supportedthere, just as if it were in a mounted slide. The precisemode of effecting this will differ, according to the particular AERANGEMENT TOR TRAifSPARENT OBJECTS. 171 plan of the instrument employed; thus in some, it is only theledge itself that slides along the stage ; in others, it is acarriage of some kind, whereon the object-slide rests; inothers, again, it is the entire platform itself that moves upona fixed plate beneath. 86. Having guided his object, as nearly as he can do bythe unassisted eye, into its proper place, the Microscopi
The microscope and its revelations . position, and supportedthere, just as if it were in a mounted slide. The precisemode of effecting this will differ, according to the particular AERANGEMENT TOR TRAifSPARENT OBJECTS. 171 plan of the instrument employed; thus in some, it is only theledge itself that slides along the stage ; in others, it is acarriage of some kind, whereon the object-slide rests; inothers, again, it is the entire platform itself that moves upona fixed plate beneath. 86. Having guided his object, as nearly as he can do bythe unassisted eye, into its proper place, the Microscopistthen brings his light (whether natural or artificial) to bearupon it, by turning the mirror in such a direction as to reflectupon its under surface the rays which are received by itselffrom the sky or the lamp. The concave miiTor is that whichshould always be first employed, the plam being reserved forspecial purposes ; and it shoiQd bring the rays to convergencein or near the plane in which the object lies (Eig. 51). The Fig. Arrangement of Microscope for Transparent Objects. distance at which it should be ordinarily set beneath thestage, is that at which it brings parallel rays to a focus; butthis distance should be capable of elongation, by the lengthen-ing of the stem to which the miiror is attached; since therays diverging from a lamp at a short distance, are notso soon brought to a focus. The correct focal adjustment ofthe mirror may be judged-of, by its formation of images of 172 MANAGEMENT OE THE MICROSCOPE. window-bars, chimrLeys, &c., upon any semi-transparent mediumplaced in the plane of the object. It is only, however, whensmall objects are being viewed under high magnifying powers,that such a concentration of the light reflected by the mirroris either necessary or desirable; for, with large objects, seenunder low powers, the field would not in this mode be equablyilluminated. The diffusion of the light over a larger area maybe secured, either by shifting the
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