62 THE PROBLEMS OF THE DEEP SEA n 



at different depths, by means of thermometers 

 specially contrived for the avoidance of the errors 

 produced by pressure, was the proof that, below 

 1000 fathoms in the Atlantic, down to the greatest 

 depths yet sounded, the water has a temperature 

 always lower than 38° Fahr., whatever be the 

 temperature of the water at the surface. And 

 that this low temperature of the deepest water 

 is probably the universal rule for the depths of 

 the open ocean is sho^vn, among others, by Captain 

 Chimmo's recent observations in the Indian ocean, 

 between Ceylon and Sumatra, where, the surface 

 water ranging from 85° — 81° Fahr., the tempera- 

 ture at the bottom, at a depth of 2270 to 2656 

 fathoms, was only from 34° to 32° Fahr. 



As the mean temjDerature of the superficial 

 layer of the crust of the earth may be taken at 

 about 50° Fahr., it follows that the bottom layer 

 of the deep sea in temperate and hot latitudes, 

 is, on the average, much colder than either of the 

 bodies with which it is in contact ; for the tem- 

 perature of the earth is constant, while that of 

 the air rarely falls so low as that of the bottom 

 water in the latitudes in question ; and even when 

 it does, has time to affect only a comparatively 

 thin stratum of the surface water before the 

 return of warm weather. 



How does this apparently anomalous state of 

 things come about ? If we suppose the globe to 

 be covered with a universal ocean, it can hardly 



