492 



DISCOVERY REPORTS 



over the glass stages. Mirrors at H and I reflect light up through the glass stages, so 

 that the plankton on the gauze may be examined in situ by the microscope. Each 

 banding is examined ; for whilst in the first place the plankton is caught only on the 

 graduated gauze, some of it is transferred to the surface of the covering banding. The 

 glass stages are ruled into squares by intersecting lines to facilitate counting; when 

 using low-power lenses the squares on the glass show through the gauze above them. 



Fig. 20. Drawing of the travelling microscope designed for use with the examination stage. The graduated 

 rod M is cut short to show the worm thread O. For further letter references see text. 



Fig. 20 shows the traversing microscope in detail. A standard microscope tube is 

 mounted on the arm / which may be moved from left to right by a rack and pinion 

 turned by the milled wheel K. The carriage L which holds the arm J is mounted to 

 slide along the two rods M and N at right angles to J and is moved backwards and 

 forwards by a worm thread O turned by the milled wheel P. Thus by turning K and P 

 the microscope may be made to cover any point of the examination stages C and D 

 The arm / and one of the rods M are marked with a series of numbered divisions so 



