METHODS OF COLLECTING AND PHOTOGRAPHING 



79 



The end of the hose may also be lowered to near the bottom and 

 may then, while pumping is in progress, be slowly drawn upward at 

 a uniform rate. In this way is pumped a vertical column of water 

 which extends from the bottom to the surface, and the volume of 

 such a column may be calculated. 



The following forms of plankton pump may be referred to 

 briefly. 



(a) Fordyce pump (Foidyce, i8g8). This invention of Professors 

 Ward and Fordyce is shown in perspective (Fig. 21) and in sec- 

 tion (Fig. 22). It "is practically a force pump. . . . The cylinder 



Lock liut 



Fig.! 



Fordyce's pump and strainer. For description see 

 text. (After Fordyce.) 



Fig. 22. Fordyce's pump in sec- 

 tions. For description see text. 

 (Aiter Fordyce.) 



of the pump is eleven by three and one-half inches and has a capacity 

 347I cubic inches per stroke. The stroke of the piston is definite 

 in length and is regulated by a lock nut as shown in the plate. The 

 valves used are finely-ground check valves, to which it is believed 

 the accuracy of the working of the apparatus is largely due. The 

 pump is connected with the water by a hose one and one-half 

 inches in diameter, whose lower end is adjusted to the various ver- 

 tical zones of water by means of attachment to a floating block." 

 For filtering the water Fordyce uses the device shown in Fig. 21, 

 at the right of the pump. This is similar to the device already de- 

 scribed in connection with the Wisconsin plankton net, and is used 

 in the same way. It is provided with a rim to which a cover of 

 wire netting may be attached to exclude foreign matter. A net 



