. The microscope and its revelations. thr objects . with the found needful. Upon this much of the finest ^ ib the ] lerii microscope depends. •ompli-l, this a good sub-stage must have rectangular,anda rack-and pillion focussing adjustment. THE SUB-STAGE I85 The vertical and lateral movements need not be as elaborate asthose of the stage, since only a small movement in each direction isrequired. The object is to secure a centring motion, a motion thatwill make the optical axis of the sub-stage combinations continuouswith the optical axis of the objective. It must therefore be a steady
. The microscope and its revelations. thr objects . with the found needful. Upon this much of the finest ^ ib the ] lerii microscope depends. •ompli-l, this a good sub-stage must have rectangular,anda rack-and pillion focussing adjustment. THE SUB-STAGE I85 The vertical and lateral movements need not be as elaborate asthose of the stage, since only a small movement in each direction isrequired. The object is to secure a centring motion, a motion thatwill make the optical axis of the sub-stage combinations continuouswith the optical axis of the objective. It must therefore be a steadymotion; the sub-stage must move decisively, and must rigidly re-main in the position in which it is left. A bad sub-stage moves in jerks, and is liable to spring from theposition intended to be final. It is not needful that the motion should lie in right lines;motion in arcs whose tangents intersect at rii/kt angles are quite asefficient. A steady, even, reliable motion that will enable a centreto be found is all that is FIG. 147.—Bocks mechanical attachable stage (1896). The focussing adjustment must be smooth, steady, and firm, actingreadily and remaining rigid. The recent employment of achromaticcondensers of wide apertures has led such critical workers asMr. E. M. Nelson to suggest a fine adjustment to the are times when it is a great luxury and a facile path todelicate and desirable results ; but it may be quite simple, a direct-action screw of fine thread, or a cone which the revolution ofa screw pushes horizontally forward upon the bottom of a slidingbar to -which the sub-stage is fixed, or an inclined plane actingin a slot in the same way. In fact, any simple device for focussingthe condenser more slowly than the rackwork will do, pushing thecondenser up to, or causing it to recede from, the under surface ofthe slide with sufficient delicacy. But no means should be employed 186 THE HISTORY AND DEVELOPMENT OF THE MICROSCOPE tor tins end whi
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
