PHYSICAL GEOGRAPHY. 289 



vast oceanic basin, which, under the tropics, extends over 145^ 

 of longitude, the Great Ocean, in contradistinction to all other 

 seas. The southern and western hemispheres (reckoning the 

 latter from the "meridian of Tenerifle) are therefore more rich 

 iw. water than any other region of the whole earth. 



These are the main points involved in the consideration of 

 the relative quantity of land and sea, a relation which exer- 

 cises so important an influence on the distribution of temper- 

 ature, the variations in atmospheric pressure, the direction 

 of the winds, and the quantity of moisture contained in the 

 air, with which the development of vegetation is so essentially 

 connected. When we consider that nearly three fourths ol 

 the upper surface of our planet are covered with water,* we 

 shall be less surprised at the imperfect condition of meteorol- 

 ogy before the beginning of the present century, since it is only 

 during the subsequent period that numerous accurate observa- 

 tions on the temperature of the sea at different latitudes and 

 at different seasons have been made and numerically compared 

 together. 



The horizontal configuration of continents in their general 

 relations of extension was already made a subject of intellectual 

 contemplation by the ancient Greeks. Conjectures were ad- 

 vanced regarding the maximum of the extension from west to 

 east, and Dicsearchus placed it, according to the testimony of 

 Agathemerus, in the latitude of Rhodes, in the direction of a 

 line passing from the Pillars of Hercules to Thine. This line, 

 which has been termed the 'parallel of the diaphragm of Di- 

 ccEarchus, is laid down with an astronomical accuracy of po- 

 sition, which, as I have stated in another work, is well worthy 

 of exciting surprise and admiration.! Strabo, who was proba- 

 bly influenced by Eratosthenes, appears to have been so firmly 

 convinced that this parallel of 36^ was the maximum of the 

 extension of the then existing world, that he supposed it had 

 some intimate connection with the form of the earth, and 

 therefore places under this line the continent whose existence 



* lu the Middle Ages, the opinion prevailed that the sea covered ^my 

 one seventh of the surface of the globe, au opinion which Cardinal d'Ailly 

 (Imago Mundi, cap. 8) founded on the fourth apocrj'^phal book of Esdras. 

 Columbus, wfho derived a great portion of his cosmographical knowledge 

 from the cai"diaal's work, w^as much interested in upholding this idea 

 of the smallness of the sea, to which the misunderstood expression of 

 " the ocean stream" contributed not a httle. See Humboldt, Examen 

 CrUiquede VHist. de la Giograpkie, t. i., p. 186. 



t Agathemerus, in Hudson, Geographi Minores, t. ii,, p. '1. Seo 

 Humboldt, Asie Cetdr., t i.. p. 120-1-2.3, 



Vol. I.— N 



