410 THE PHYSICAL GEOGRAPHY OF THE SEA. 



up to tlie stars in a cloudless sky, and serve to lower the temper- 

 ature of the surface-waters, by radiation, two degrees. Here, then, 

 is a difference of four degrees, which we will suppose extends 

 only ten feet below the surface. The total and absolute change 

 made in such a mass of sea water by altering its temperature two 

 degrees is equivalent to a change in its volume of three hundred 

 and ninety thousand millions of cubic feet. And yet there are 

 philosophers who maintain (§123) that evaporation and precipita- 

 tion, changes of temperature and saltness, and the secretions of in- 

 sects, are not to be reckoned among the current-producing agents 

 of the sea — that the gentle trade- winds do it all ! 



759. Do not the clouds, night and day, now present themselves 

 Day and night, to US lu a ucw light? Thcy arc cogs, and rachets, 



and wheels in that grand and exquisite machinery which governs 

 the sea, and which, amid all the jarring of the elements, preserves 

 the harmonies of the ocean. 



760. The log-books of not less than 1843 vessels cruising on 

 Lo-3 overhauled for ^hc polar sidc of 35° S. havc, by the officers of the 

 kelp and ice. Obscrvatory, been overhauled for kelp and ice. Of 

 these, 367 — or one in five — mentioned kelp or sea-weed east of 

 Cape Horn ; 142 mention "rock-weed and drift matter" between 

 the previous meridian and 10° W, and chiefly between 35° and 40° 

 S. " Long kelp" is also found by Australian traders after passing 

 the Cape of Good Hope ; 146 logs make mention of it between the 

 meridians of 40° and 120° E. It most abounds along this line, how- 

 ever, between the meridians of 45° and 65° E., and the parallels of 

 42° and 48° S. These sargassos are sketched with a free hand on 

 Plate IX. 



761. Sea-weed is frequently mentioned also by the homeward- 

 A Parsa^so in the bo^nd Australian traders on their way to Cape 

 South Pacific. Horn : this collection has (§ 139) already been al- 

 luded to. It now appears that instead of three, there are really 

 five true sargassos, as shown on Plate IX. 



762. The weedy space, marked as such, about the Falkland Isl- 

 sea-wee<i about the ^^ds, is probably uot a true sargasso. The sea- 

 Faikiand Islands. wccd icportcd thcrc probably comes from the Straits 

 of Magellan, where immense masses of it grow. These straits are 

 so encumbered with sea-weed that steamers found great difficulty 

 in making their way through it. It so encumbers their paddles as 

 to make frequent stoppages necessary. 



