ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



547 



the lower end of the limb is a hinge, which permits it to be vertically 

 rotated through 90°, so that the tube-axis can be brought parallel to the 

 stage. In this position the instrument can be used as a cathetometer, 

 or Microscope for reading vertical distances, especially for such subjects 

 as plant-growths which could be estimated by the eye-piece micrometer 



Fig. 127. 



Fig. 128. 



measurements. A millimeter scale could be engraved on the triangular 

 bar. Below the stage the pillar has a rotation hinge which enables the 

 optical part to be used with greater freedom (fig. 128). 



The instrument can also be conveniently used as an aquarium Micro- 

 scope, but it would be an improvement to lengthen the lower end of 

 the tube. 



Even when the instrument is used, as a preparation Microscope the 

 double hinging is useful, as it facilitates search over the field. 



Koristka's Mechanical Stage.* — This accessory is shown in fig. 129. 

 The movements in the two directions are 80 mm. and 40 mm. respec- 

 tively, and the two divided scales are provided with verniers, which 



* F. Koristka's Catalogue, Milan, p. 54. 



