30 Temperature of the Ocean. 



the presence or absence of certain plants and animals, the power 

 of adaptation more or less inherent in all living organisms, as 

 well as the accumulative tendency of climatic conditions, the 

 influence of oceanic currents upon climate, and hence indirectly 

 upon the development of the fauna and flora in any given 

 region, seems to afford an ample basis to account for the 

 former presence of tropical species in latitudes now subjected 

 to the rigours of a cold climate, and for the existence in 

 past geological times of arctic forms in regions at present 

 belonging to the temperate zone. In endeavouring to explain 

 these anomalies of climate, it appears hardly necessary to go in 

 search of vast cosmic changes, such as an alteration in the 

 position of the terrestrial axis, a diminution in the amount of solar 

 heat, a gradual cooling of the earth's crust, which, if they have 

 occurred — and we have as yet no positive evidence in their 

 favour — would imperil the existence of all life on our planet ; 

 while we have, close at hand, an agency whose effect upon 

 climatic conditions may be said to be a matter of daily experi- 

 ence, and which is sufficiently powerful to establish, in almost 

 any region on the earth's surface, the small difference of tem- 

 perature which is a decree of life or of death to numerous animal 

 and vegetable organisms. 



Deep-sea Temperature. — We are indebted to the officers of 

 the United States Coast Survey for the first systematic investi- 

 gation of the conditions of temperature below the sea-surface. 

 Their operations, extending over fourteen years, from 1845 to 

 1849, determined the course of the two great currents which, 

 under the name of the Gulf Stream and the Labrador 

 Current, were known to flow along the United States coast 

 between Nantucket Island and the Gulf of Mexico. Although 

 not provided with the more perfect appliances and instruments 

 placed at the disposal of recent . explorers, their observations 

 furnished ample evidence of the existence below the sea-surface 



