58 THE MICROSCOPE 



the under surface of this plate is pivoted a similarly 

 curved plate, fitted with three tubulures, each of which 

 carries an objective. By rotating the lower plate each 

 of the objectives can be brought successively in to the 

 optical axis of the microscope. 



FIG. 49. Eye shade. 



For critical work and particularly for photo-microg 

 raphy, however, the interchangeable nosepiece is by 

 no means perfect as it is next to impossible to secure 

 accurate centreing of each lens in the optical axis. 

 For special purposes, therefore, it is necessary to employ 



FIG. 50. Double nosepiece. 



FIG. 51 Triple nosepiece 



a special nosepiece such as that made by Zeiss or Leitz 

 into which each objective slides on its own carrier and 

 upon which it is accurately centred. 



Warm Stage (Fig. 52). This is a flat metal case 

 containing a system of tubes through the interior of 

 which water of any required temperature can be cir- 



