218 PHYSICAL GEOGRAPHY OF THE SEA, A'ND ITS METEOROLOGY. 



are raised for contemplation merely; they cannot be answered 

 now ; they grow out of some of the many grand and imposing 

 thoughts suggested by the study of the revelations which 'the 

 hydrometer is already beginning to make concerning the wonders 

 of the sea. ^ Eeturning from this excursion towards the fields of 

 speculation, it will be perceived that these observations upon the 

 temperatm-e and density of sea water have for then- object to weigh 

 the seas, and to measm-e in the opposite scales of a balance the 

 specific gravity of the waters of one hemisphere with the specific 

 gravity of the waters of the other. This problem is quite within 

 the compass of this exquisite sj'stem of research to solve. But, in 

 order to v/eigh the seas in this manner, it is necessary that the little 

 hydrometric balance by which it is to be done should be well and 

 truly adjusted. 



448. From these premises it would not be difficult to show that 

 Amount of salt in, the saltucss of the sca is a physicpJ necessity. In 

 gravurof Sr'^*^ some of the aspects presented, the salts of the sea 

 ^^■^^<^^- hold the relation in the terrestrial mechanism that 



the balance-wheel does to the machinery of a watch. Without 

 them the climates of the earth could not harmonize as they do ; 

 neither could the winds, by sucking up vapour, hold in check the 

 expansive power of tropical heat upon the sea ; nor counteract, by 

 leaving the salts behind, the thermal influence of the sun in im- 

 parting dynamical force to marine cmTents ; nor prevent the solar 

 ray fi'om miduly disturbing the aqueous equilibrium of our planet. 

 As evaporation goes on from a sea of fresh water, the level only, 

 and not the specific gravity, of the remaining water is changed. 

 The w^aters of fresh intertropical seas would, instead of growing 

 heavy by reason of evaporation between the tropics, become lighter 

 and lighter by reason of the heat ; while the water of fresh polar 

 seas would grow heavier and heavier by reason of the cold — a con- 

 dition which, by reason of evaporation and precipitation, is almost 

 the very reverse of that which natm-e has ordained for the salt sea, 

 and which, therefore, is the wisest and the best. The average 

 amount of salts in sea water is not accm-ately known. From such 

 data as I have, I estimate it to be about 4 per cent. (.039), and the 

 mean specific gravity of sea water at 60^ to be about 1.0272. Sup- 

 posing these conditions to be accurate — and they are based on data 

 which entitle them to be considered as not veiy wide of the mark — 

 the hydrometer and thermometer, with the aid of the table (§ 441), 

 will give us a direct measure for the amount of salt in any specimen 



