THE CLIMATES OF THE SEA. 383 



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 hea\y, 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-regu- 

 lating, self-compensating pendulum, beating time in the sea to 

 the seasons of the year. 



722. Sea and land climates contrasted. — In seeking information 

 concerning the climates of the ocean, it is well not to forget this 

 remarkable contrast 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 dr}^ land after the winter " is past 

 and gone," the solid parts of the earth contimie 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 ivaters— not the ice — of the sea are annually subjected, 

 and therefore the isotherms of 40°, 50°, 60°, 70°, and 80° have been 

 drawn for March and September, the months of extreme heat 

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

 responding isotherms for any other month will fall between 

 these, taken by pairs. Thus the isotherm 70° for July will fall 

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



