4 68 THE POPULAR SCIENCE MONTHLY. 



another, even in places of the same parallel of latitude. One or 

 two examples may be taken to illustrate these points. The, tem- 

 perature off Rio Janeiro in latitude 20 south was found by the 

 Challenger to be 0'6 C. at a depth of 2,150 fathoms. In a similar 

 latitude north of the equator at a depth of 2,900 fathoms the tem- 

 perature was found to be 2'2 C., and at a point near Porto Rico 

 there is a deep hole of 4,561 fathoms, with a bottom temperature of 

 2-2 C. 



Again it has been shown by the American expedition that the 

 temperature of the water at the deepest point in the Gulf of Mexi- 

 co, 2,119 fathoms, is the same as that of the bottom of the Straits of 

 Yucatan, 1,127 fathoms, namely, 4'1 C. And, passing to another 

 part of the world altogether, we find in the small but deep sea that 

 lies between the Philippines and Borneo that, at a depth of 2,550 

 fathoms, the temperature is 10 '2 C. These facts then show that, 

 although at the bottom of the deep seas the water is always very 

 cold, the degree of coldness is by no means constant in the same 

 latitude for the same depth. 



We must now return to the polar currents. We have assumed 

 above that these currents do exist, and it is probable that by this 

 time the reader must have seen why they are assumed to exist- 

 The water at the bottom of the ocean is exceedingly cold. Where 

 does this coldness come from ? It is obvious that in temperate and 

 tropical climes it does not come from the surface. Nor is it at all 

 probable that it comes from the earth upon which the water rests ; 

 for, if it were so, the temperature for water of a given depth would 

 always be the same. We should not find the bottom temperature 

 of 2'4 C. at 2,900 fathoms off Rio de la Plata and a temperature of 

 2'2 F. in 4,561 fathoms off Porto Rico. 



In fact, the only hypothesis that can with any show of reason be 

 put forward to account for the temperature of the bottom of the 

 ocean is that which derives its coldness from the polar ice. 



Perhaps it is of the nature of an assumption to say that there 

 are no rapid currents and tides in the abysmal depths of the ocean, 

 for we have no means of demonstrating or even of calculating the 

 rate of flow of these waters. But it is a reasonable hypothesis and 

 one that we may well use until the contrary is proved. 



A fact of some importance that supports this hypothesis, as re- 

 gards some parts of the ocean at least, is presented by the sea-anem- 

 ones. Many of the shallow- water actinians are known to possess 

 minute slits in the tentacles and disk, affording a free commu- 

 nication between the general body cavity or coelenteron and the 

 exterior. In many deep-sea forms the tentacles are considerably 

 shorter and the apertures larger than they are in shallow-water 

 forms. It is difficult to believe that such forms, perforated by, 

 comparatively speaking, large holes, could manage to live in rapid- 



