368 PHYSICAL GEOGEAPHY OF THE SEA, AND ITS METEOROLOGY. 



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

 The vibrations of north havo been tempered, and been made warm 

 the Gulf Stream. ^^^ ^jg^^ ]jy ^he 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 

 pendulum, beating time in the sea to the seasons of the year. 



722. In seeking information concerning the climates of the 



Sea and land climates ocean, it is Wcll UOt tO forgOt this remarkable con- 

 contrasted, -i^j-g^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 dryland, 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, con- 

 sequently 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 atmosphere above begin to dispense with their heat faster 

 than the rays of the sun can impart fresh supplies, and conse- 

 quently, the climates which they regulate grow cooler and cooler 

 until the dead of the winter again. But at sea a different rule 

 seems to prevail. Its waters are the store-houses * in which the 

 surplus heat of summer 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 IV. is intended to show the extremes of heat and cold to 

 which the waters — not the ice — of the sea are annually subjected, 

 and therefore the isotherms of 40'', 50°, 60', 70'', and SO'' have been 

 drawn for March and September, the months of extreme heat 

 and extreme cold to the inhabitants of the " great deep." Cor- 

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



