METABOLISM IN THE SEA 185 



unreasonably, be compared with Lord Kelvin's 

 estimation of the age of the habitable earth 

 founded on experiments made on the cooling of 

 certain rocks from high temperatures. These 

 results, though only approximations, gave at least 

 an approximate measure of the age of the globe, 

 and prevented " unlimited drafts on the bank of 

 time." Henson's results give at least a sufficient 

 quantitative idea of the contents of the sea to 

 enable us to arrive at results of extreme theoretical 

 and practical interest. 



All these investigations, the " tow-nettings " of 

 the older naturalists and the newer Hensen and 

 other quantitative methods, have furnished us with 

 a mass of information relating to microscopic life 

 in the sea, which, merely to summarize, would be 

 beyond the compass of a work like this. We may 

 note only a few salient points. The varying 

 distribution of the plankton according to the season 

 was one of the first things to be made out. 

 Speaking in general terms only, a series of tow- 

 nettings made on (say) the north-west coast of 

 England, at the surface of the sea, would present 

 a sequence approximately as follows : early in the 

 year, in January and possibly February, there 

 would be a general scarcity of life, but about the 

 end of the latter month, or perhaps later, according 

 to the season, we should expect to meet with an 

 increase in the bulk of the plankton. This is the 

 beginning of the " seedtime " of the sea, fishes and 



