Dr. Carpenter's Lecture. 89 



water much colder than the mean winter temperature of the latitude 

 must have a northerly, whilst water that is wanner must have a 

 southerly, source. In accordance with this we find that most of the 

 animals of the cold area, such as the beautiful Comatula EschricMii, 

 belong to the boreal fauna; whilst British species, such as the common 

 Solaster papposa. which is dwarfed from the size of a plate to that of 

 a crown-piece, are much stunted. Yet the fauna is abundant, as no 

 temperature seems to prevent life, so long as sea- water is liquid. 

 Pressure, though enormous, will not affect vital functions ; since an 

 animal, whose cavities contain air in aqueous solution only, can con- 

 tract and expand just as well with a pressure of three tons to the 

 square inch as it can on the surface. Not but what change of pres- 

 sure, brought on by sudden removal, might produce some derange- 

 ment. Neither temperature nor pressure, then, being directly of 

 supreme importance, it is the supply of oxygen which has most 

 influence on Animal Life in the deep seas. This is regulated by the 

 general flow of water near the sea-bottom, — a flow not confined to 

 any particular passage or area, but maintained by difference of 

 specific gravity, produced by difference of temperature. As sea- 

 water, in this respect differing from fresh- water, continues to increase 

 in density down to its freezing-point, which is 27° F. if agitated, and 

 25° F. if still, the Polar column will outweigh the Equatorial column, 

 and there will be a lateral outflow at the bottom towards the equa- 

 torial area. This will cause a lowering of water in the polar area, 

 and produce a surface-flow of water from the Equator towards the 

 Poles. The two bottom-flows from either pole will thus meet near 

 the Equator, and rising, will bring cold water nearer to the surface 

 there than anywhere else, except where the surface itself is subjected 

 to cold. In this way the bottom-temperature of the South Atlantic 

 would be lower than that of the North Atlantic, by reason of the 

 less restricted body of the polar flow in the former. The tables 

 given in the "' Challenger's " report confirm the conclusions thus 

 arrived at. From these we find that the general temperature of the 

 North Atlantic bottom is about 351° or 36° F., decreasing to 34° F. 

 near St. Thomas, and under the Equator itself to 324° F., the lowest 

 temperature of all. This section proves that the South Atlantic 

 under-flow extends north of the Equator, as had been previously 

 surmised by the lecturer. Only one section was made in the South 

 Atlantic, and no temperatures lower than 33^° F. were there obtained, 

 the expedition not happening to hit upon the channel which brought 

 in the water at 32*4° F, found under the Equator. Most remarkable 

 of all is the line of 35° F. which can be traced across the South 

 Atlantic and then gradually slopes down in the North Atlantic till 

 it is lost. The temperature of the North Atlantic depths is pro- 

 bably about 3° F. higher than in the South Atlantic. Off the coast 

 of Lisbon, in lat. 38° N., the line of 40° F. is found at 700 to 800 

 fathoms ; in lat. 22° N. at 700 fathoms ; and on the Equator at 300 

 fathoms only, descending from a surface temperature of 75° F. 

 The reason for this has been already shown to be the continual rise 

 of the Polar under-flow towards the surface in the Equatorial belt. 



