i8 The Voider-Water World 



creatures known collectively as " Plank- 

 ton " varies greatly in quantity at any 

 given spot, according to the fluctuations 

 of temperature and ocean currents. At 

 one moment the sea surface in a given 

 area may swarm with this floating life, 

 whilst a few hours later scarcely a single 

 individual will fall to the tow net. The 

 direct heat of the sun, the light of the 

 moon, and the tranquillity or turbulence 

 of the water may all have an influence 

 on these delicate organisms. In the 

 tropics the plankton tends to sink below 

 the surface during the heat of the day, 

 whilst at night it swarms at the surface, 

 causing the phosphorescence which may 

 occasionally be observed in home waters. 

 Our west country fishermen at such 

 times speak of seas as " burning " and 

 believe the phosphorescence to be caused 

 by the friction of the minute salt particles. 

 They may then refer to the sea as being 

 " dirty," and, indeed, when plankton is 



