ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 479 



Third. It is inexpensive in construction. An objection is sometimes 

 made that one side of the stage-plate is moved, while the other is not, 

 thus elevating one side more than the other. We only ask those to 

 whom this may appear an objection, to make a practical and careful 

 test. They will find that this objection is utterly invalid in practice, as 

 the range of the motion required is very slight." 



On the other hand it must be pointed out that this system of fine- 

 adjustment is hardly tolerable for any but rough-and-ready elementary 

 work, as the continual tilting of the stage-plate supporting the object 

 renders the employment of suhstage apparatus very inconvenient, not to 

 say practically impossible. 



Aruici adopted this mechanism in one of his models we have met 

 with, one of which is shown in fig. 64, where the stage consists of a 

 plate bent on itself, tho upper half being pressed upwards by a screw, 

 returning by its own " spring " when the screw is withdrawn. The 

 more common form is that shown in figs. 65 and 66, where the stage 

 does not consist of one plate bent on itself, but of two joined by a 

 short bar at one end. A peculiar modification of this plan is shown in 

 fig. 67, where the thick stage has a thin plate separated from its upper 

 surface, which is raised at one end by a screw, as in the other cases. 

 Fig. 68 shows another modification, adopted by Seibert, of Wetzlar, 

 the stage being suspended between two pivots at one end and tilted 

 by a screw at the other end, acting against the pressure of a spiral- 

 spring. 



Amici also adopted the system of suspending the stage (fig. 69) 

 on pivots on either side of the pillar, an angle-piece being connected 

 at the back forming a bent lever, by which the stage was tilted by a 

 screw acting against a spring. Nobert modified this latter system, even 

 with his largest Microscopes to which he applied his stage-micrometer, 

 by suspending the stage on pivots on either side of the pillar, and at- 

 taching the angle-piece beneath the stage so as to be acted upon by a 

 screw passing through the pillar ; the downward motion of the stage 

 acted by gravity only as in the small French Microscope shown in 

 fig. 70, which instrument has in addition a peculiar crank-arm attached 

 near the edge of the milled head, which raises and lowers the body-tube 

 instead of the usual rack and pinion. This plan has been adopted in 

 many of the commoner types of Microscopes issued in recent years in 

 Germany, in some cases (as in the Microscope by Schieck, of Berlin, 

 shown in fig. 71) the downward motion of the stage is controlled by a 

 spiral-spring pressing on the front of the angle-piece. 



Trecourt and Oberbiiuscr (fig. 72) avoided the tilting of the stage 

 by making the upper plate move up or down in a horizontal position 

 by means of a screw and socket at one end and a guide-pin at the other 

 end. Charles Chevalier and others in France adopted this mechanism, 

 with more or less modification; and in England, Pritchard, Carpenter 

 and Westley, and others also employed the system. Fig. 73 shows the 

 application of a rack and pinion with a guide-pin giving parallel motion 

 to the upper stage-plate. This focusing by the stage was subsequently 

 elaborated by the late Hugh Powell, for which he was awarded a silver 

 medal by the Society of Arts in 1841, and which consisted in making 

 the upper part of the stage, carrying the " Turrill " mechanism, to move 

 upwards or downwards in tho strictly horizontal position by a system of 

 screws acting upon levers and wedges. Andrew Koss appears to have 

 adopted this system also in some of his early constructions. 



