382 THE PHYSICAL GEOGRAPHY OF THE SEA. 



721. In September, when the waters in the cold regions of the 

 The vibrations of the ^orth havc been tempered, and been made warm 

 Gulf stream. ^^^ light bj the heat of summer, its limits on the 

 left are as denoted by the line of arrows (Plate VI.) ; but after 

 this great sun-swing, the waters on the left side begin to lose their 

 heat, grow cold, become heavy, and press the hot waters of this 

 stream into the channel marked out for them. Thus it acts like 

 a pendulum, slowly propelled by heat on one side and repelled by 

 cold on the other. In this view, it becomes a chronograph for the 

 sea, keeping time for its inhabitants, and marking the seasons for 

 the great whales ; and there it has been for all time vibrating to 

 and fro, once every year, swinging from north to south, and from 

 south to north again, a great self-regulating, self-compensating 

 liquid pendulum. 



722. In seeking information concerning the climates of the 



sea and land climates OCCaU, it is WCll not tO forgCt' this rcmarkablc con- 

 contrasted. ^^j^g|. between its climatology and that of the land, 

 namely : on the land February and August are considered the 

 coldest and the hottest months ; but to the inhabitants of the sea, 

 the annual extremes of cold and heat occur in the months of March 

 and September. On the dry land, after the winter " is past and 

 gone," the solid parts of the earth continue to receive from the 

 sun more heat in the day than they radiate at night, consequently 

 there is an accumulation of caloric, which continues to increase 

 until August. The summer is now at its height; for, with the 

 close of this month, the solid parts of the earth's crust and the at- 

 mosphere above begin to dispense with their heat faster than the 

 rays of the sun can impart fresh supplies, and, consequently, the 

 climates which they regulate grow cooler and cooler until the 

 dead of winter again. But at sea a different rule seems to prevail. 

 Its waters are the store-houses'^^ in which the surplus heat of sum- 

 mer is stored away against the severity of winter, and its waters 

 continue to grow warmer for a month after the weather on shore 

 has begun to get cool. This brings the highest temperature to 

 the sea in September, the lowest in March. Plate TV. is intended 

 to show the extremes of heat and cold to which the ivaters — not 

 the ice — of the sea are annually subjected, and therefore the iso- 

 therms of 40°, 50°, 60°, 70°, and 80° have been drawn for March 



* Vide Chap. XXII., Actinometry of the Sea. 



