148 Transactions of the Society. 



a horizontal position, as for photography, a very great degree 

 of rigidity being thereby secured in the position where it is 

 most required. The height required for this foot or support is 

 kept low by hinging the limb about an axis placed only 78 mm. 

 (3 inches') above the base ; this axis is made very massive, in order 

 to secure both ample stiffness and to provide a large bearing sur- 

 face, so that, with a good fit, the friction is sufficient to sustain 

 the limb at any angle, more especially since the position of the 

 axis is such as to bring the centre of gravity of the inclinable por- 

 tion of the instrument vertically above the axis at an inclination 

 which only differs slightly from 60°, according to the position of 

 the stage. In the vertical position, the limb itself bears against a 

 recess suitably formed in the base. In practice, the entire instru- 

 ment may be readily carried about by means of the handle provided 

 in the limb, without fear of displacing anything — even with a high- 

 power objective, the focus remains in adjustment. The limb itself 

 is made of a deep T-girder section, the broad flange of the T forming 

 the bearing for the large dovetailed slide which carries the stage, 

 and also providing a rigid attachment for the tube. The depth of 

 the T is proportioned to the bending stresses likely to be developed 

 by the weight and manipulation of the instrument, the back of the 

 limb thus assuming a curved outline. The web of the T section is 

 cut away in two large openings, thus saving weight and reducing 

 the whole limb to a close approximation to a rigidly braced girder, 

 while one of the openings provides a most convenient handle, by 

 which the entire instrument may be safely lifted. 



The Stage. — The stage is carried by a stiff bracket attached to 

 a massive slide, moving, by rack and pinion, along the broad flange 

 of the limb ; the milled heads attached to the pinion — which consti- 

 tutes the coarse-adjustment of the Microscope — are carried on long 

 stout stems, so as to clear the base when the stage is racked down ; 

 in the vertical position the separation available between the end 

 of the body-tube and the stage surface is 95 mm. (3f in.), while if 

 the instrument be slightly inclined, tins may be increased tu 

 120 mm. (4| in.). An important advantage of the construction 

 here described lies in the fact that the relative position of stage 

 and tube is as rigidly secured with the largest separation as when 

 the stage is close up to the tube ; in the older instruments, as 

 soon as the body-tube is racked up to any considerable extent, 

 the bearing between tube and limb is reduced, and a serious amount 

 of looseness results. 



The stage bracket carries at its outer end, concentric with the 

 optic axis of the instrument, the fine adjustment. The details and 

 construction of this portion of the instrument are exactly similar 

 to any good fine-adjustment, except that the whole arrangement is 

 inverted, and the moving plunger carries the stage direct. The 

 great advantage of this arrangement is that all the weight that 



