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SUMMARY OF CURRENT RESEARCHES RELATING TO 



has tlie " Society " screw at the lower end for use with low powers. 

 Mr. Tolles also applies the extra optical combination required for 

 an erecting eye-piece in this position, and also his various forms of 

 amplifiers — simple and compound. 



The substage has a slight lateral swivel motion that enables the 

 observer to direct the condenser very exactly radially upon the object, 

 or to use various portions of the minute condensed cone of light, and 

 it also compensates for the varying thickness of the object-slides by 

 which the lateral circular track of the condenser may be rendered not 

 quite concentric with the object. (We are informed by Mr. Tolles 

 that to the earliest forms of his traversing substage-bar he provided 

 special means to secure the exact radial direction of the illuminating 

 pencil concentric with the object with different thicknesses of object- 

 slide ; he has forwarded a photograph of a Microscope thus constructed 

 by him in 1873.) 



Two stages are supplied that are interchangeable by a simple 

 spring latchet arrangement, clipping them on the same fixed centering 

 ring attached at right angles to the vertical disk. The one stage 

 (in situ in the figure above referred to) is shown in Fig. 8, half size. 



Fig. 8. 



It rotates completely. The rectangular plate of German silver is 

 about -^ inch in thickness, and is attached to a glass friction-plate, 

 held against the circular stage by an adjustable spring pressure-point ; 

 the thickness of this metal plate forms no hindrance to the use of the 

 hemispherical lens, seen in the centre, which is intended to be used 

 in immersion contact with the base of the object-slide. 



The mechanical stage (Fig. 9) presents several points of novelty. 

 The rectangular motions are controlled on the surface of the stage 

 entirely within the circumference. The milled head on the right is 



