INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 1073 



All of the stages are reversible on the stand, thus admitting of 

 unlimited obliquity, and still keeping the object in the centre of the 

 swinging bar. 



(2) Histological. — This, constructed in 1876 (Fig. 137), shows the 

 adaptation of the swinging substagc to a cheai) form of Microscope, 

 and was earlier in date to that which wo recently described at p. 532 

 as being the first cheap form that we had seen. 



Mr. Zentmayer also constructed two other forms intermediate 

 between this and the Centennial (" U.S. Army Hospital stands "). 



Bulloch's Congress and Biological Microscopes. — (1) Congress 

 {older form). — -In 1877 the form shown in ^ scale in Figs. 138 and 139 

 (19 inches high) was brought out (patented in 1879). 



The figures render any detailed description of the parts of the 

 instruments unnecessary, with the exception of the substage and mirror 

 arrangements. These both move about the same centre, which is at a 

 jjoint the thickness of an ordinary slide above the stage, and they can 

 be rotated by hand above and below the stage either together, when 

 connected by the spring stop S (Fig. 138j, or separately (as shown in 

 Fig. 139). 



The two arms (DD and E) carrying the substage and the 

 mirror are attached to the graduated cii'cles shown in the figure, by 

 which the exact degree of obliquity can be registered. 



As originally constructed by Mr. Bulloch, the end of the substage 

 pinion (passing through the limb) was provided with a toothed wheel 

 A, upon which the tangent screw B acted, producing the lateral 

 rotation of the substage bar. This mechanical rotation has since been 

 replaced by friction motion that can be clamped by the milled head 

 shown on Fig, 140 in the place of A in Fig. 138. 



When placed horizontally as f(U' drawing, every part moves 

 accurately about the same centre X (in direct line with the object on 

 the stage). 



The fine adjustment is on the Franco-German princii)le, and 

 moves the entire body without changing the distance between the 

 objective and the cyc-piccc. The levers 11 II act directly upon the 

 sliding-box wliicli contains the pinion of the coarse adjustment, and 

 this is in turn pressed down by a strong spiral spring J above it. In 

 addition (wliich is important with tliis form of fine adjustment) the 

 Society screw at the end of the body is nrrimged as a safety nose- 

 piece K with spring. The arnuigcnu^nt of this form of fine adjust- 

 ment difiers from that of Mr. Zentmayer, as the latter uses an 

 independent slide for the coarse and for the fine adjustment, and not 

 one slide for btitli. 



Heretofore in centering the stage to the optical axis it has been 

 d(mc by a ring within aiiotlier one, in which the screws (»perate eitlier 

 to draw or pusli the iuttTior ring into position. By this metliod the 

 stage, in order to uso it for obliipu! light, has to bo made inincces- 

 sarily largo. In place of a complete ring. ]Mr. Bulhxdi therefore 

 uses a segment or " saddlu piece," to which tlie stage ring is attached. 

 Tlie amingcment is sliown in the upper section of Fig. l;!8, where F 

 is the saddle-pieie, witli tlie four centering screws putisiug through 



