30 



THE LAST CRUISE OF THE CARNEGIE 



"plankton-pump." This apparatus is lowered to various depths 

 to count the number of microscopic animals and plants existing 

 at each water-level. Due to an insuflSciency of power, our bio- 

 logical work was limited to the study of these minute, drifting 

 organisms found everywhere in the oceans. A small conical net 

 made of very fine-meshed silk bolting-cloth, such as millers use 

 in sifting flour, is attached to the end of the bronze cylinder. 

 A pump actuated by a falling lead weight forces a measured 



The Stevenson Meteorological Shelter 



On the quarter-deck housing instruments to measure temperature and humidity of 

 the air. 



volume of sea-water through the net. One has only to lower the 

 apparatus to the desired depth, drop a brass "messenger" down 

 the wire to release the catch on the pump, and gravity does the 

 rest. The cylinder is closed while being lowered and raised. 

 This avoids contamination of the desired sample by plankton 

 living in the upper layers of the water. 



From this description, the plankton-pump seems to be a clever 

 little mechanism which does its appointed task uncomplainingly. 



