226 



DEPTHS OF THE OCEAN 



Conduction 

 of heat. 



the maximum temperature has been reached, but already on the 

 loth June (1903) the water of this poll is seen to be 5° C. 

 warmer at a depth of 2 metres than at the surface. 



To understand how such a high temperature can be preserved 

 for a length of time at a depth of 2 metres, one must bear in 

 mind the fact that the conduction of heat plays an altogether 

 subordinate part in the thermal conditions of the sea. Kelvin 

 and Wegemann have made some calculations on the trans- 

 mission of heat in water by conduction ; Wegemann commences 

 with a sea 5000 metres deep, with a temperature of 0° C. 

 throughout ; the surface is supposed to be in contact with a 



Fig. 158.— The Vertical Distribution of Temperature [t) and Salinity {s) 



IN THE KvERNE-POLL, IOTH JUNE I903. 



source of heat at a temperature of 30' C. No forces inter- 

 vening other than conduction, no heating effect would be 

 perceived at a depth of 100 metres after 100 years, and after 

 1000 years the temperature at 100 metres would only have 

 reached j.^, C, and at 200 metres 0.6° C. It is thus seen 

 that transmission of heat by conduction is practically negligible 

 in the sea. The heat conveyed by the sun to the uppermost 

 water-layers cannot therefore be propagated into deep water by 

 conduction, but only through movements of the water — waves, 

 currents, convection "currents," etc. Where there is no such 

 motion, and where the sun's rays cannot penetrate, heat cannot 

 be transmitted by conduction, and hence we find temperatures 

 as low as 2" C. or less in deep water even under the equator. 



