946 SUMMARY or CURRENT RESEARCHES RELATING TO 



plate C, and, travelling along the rack, gives vertical movement to 

 the plate D, and also to the plate F on which the object-slide is 

 placed. F and F' are in one piece or connected. The i)inion head 

 B controls the hollow arbor surrounding A, and forms part of h, 

 which gears into the toothed face of F' and gives horizontal motion 

 to F and F' — the upper plate (at F') slides in a 

 Fig. 223. groove in the plate D bent upwards from this 



latter, and solid with it. 



A, a, and D are made to work independently, 

 and would be unaffected if all the mechanism of 

 the horizontal motion were removed, i. e. there is 

 no friction between the two arbors or parts. The 

 milled head, arbor, and pinion A, are held firmly 

 in D by the flange g, and by the pinion itself; 

 the required tightening is given by the screw 

 shown in the lower end of the arbor, and the 

 pinion itself is shouldered on and clamped to 

 the arbor. 

 Fig. 223 shows a top view of the box, or bearing, within which 

 the hollow arbor E works, attached to the vertical moving plate D. 



The special feature of the improved stage appears to be the gain in 

 rigidity by the application of the rim or flange above the general plane 

 — indeed it would now appear that the flexure, hitherto a serious 

 drawback in all mechanical stages permitting a large range of obliquity 

 of incidence beneath, is thus practically overcome. The new shaped 

 rim does not in any way interfere with the rectangular and rotatory 

 motions of the stage, whilst, instead of adding to the thickness of 

 metal beneath the plane of the object, it has, on the contrary, enabled 

 Mr. Tolles to reduce this perpendicular thickness to practically 

 nil. The hemispherical immersion illuminator is applied to the 

 under surface of the rotating plate C by a screw thread ; the plane 

 surface of the lens is then flush with the surface of the object-plate 

 F, and the stage is so thin that upwards of 160° of the hemi- 

 spherical surface is exposed beneath ; dark field illumination could 

 thus be obtained, even with Powell and Lealand's homogeneous- 

 immersion I of 1 -47 N. A. (150° in crown glass). 



Goodwin's Growing-slide. — This slide was designed by Mr. W. 

 Goodwin with the view of obtaining one in which the objects should 

 be capable of being placed as much as possible under normal conditions 

 as regards the supply of water, &c. 



It consists (Fig. 224) of a triangular plate of glass A, the sides of 

 which are the ordinary length of a slide (3 inches). Upon this are 

 cemented three pieces of ebonite a, the inner surfaces of which are cut 

 in a curve so as to allow a thin glass cover h to lie freely but closely 

 between them. There is an indiarubber band c round each stop which 

 projects a short distance across the cover, and prevents any movement 

 of the latter when once placed in position. In the centre of the cover 

 a small hole d is drilled, and round this hole is a metal ring e. Under 

 the edges of the cover are placed three threads /. 



The action of the slide is as follows : — Placed in a horizontal 



