INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 



1071 



freedom of motion not obtained by any other arrangement. Owing to 

 its simplicity, convenience, and durability, it has been extensively 

 copied at home and abroad. The stage may be detached with facility, 



Fig. 135. 



by simply unscrewing the nut at the back Fig. 136. 



of the bar, to be replaced by another 

 stage, as, for instance, the Mechanical 

 stage or the Diatom stage." 



2nd. The Mechanical stage (Fig. 135, 

 lialf-size) is 4 inches square and -^^ 

 inch thick, with rectangular movements 

 of 1 inch by the milled heads shown 

 on the right and left. The forward 

 motion of the stage is by means of a fine 

 chain winding on a spindle beneath the 

 stage acted on by the outer milled head, 

 and is provided with a set-screw by 

 which any stretching of the cliuin can be 

 at once compensated. The cross-motion 

 is effected by a travelling scrow-sockot 

 attached beneath the stage, acted on by 

 the inner milled head. These movements 

 are extremely well constructed by Mr. 

 Zentmaycr. The graduated scales shown 

 at tlie base serve as a finder. 



The central circular plate (graduated at the margin) rotates in tho 

 jdane of tlio stage, an<l is provided with two clips for the object. 

 Inasmuch as this rotating cciitre-pieco moves out of centre with every 



•1 n 2 



