CURVE OF EARTH'S SURFACE 15 



of the barometer and the depth of water in the harbour. He 

 found extrêmes for the former were 767" 75 and 75079 milli- 

 mètres, corresponding to the water depths of 6,309 and 6,538 

 millimètres. Hère the variation corresponds closely to the 

 différence in spécifie gravity between mercury and the sea- 

 water — that is, according- to the above records, = 13' 5. 



Careful modem coastal surveys show no marked différences 

 in sea-level ; those recorded do not exceed half a mètre. 

 Surveys Connecting up the coast of the Atlantic near New 

 York with that of the Pacific near Seattle show a différence of 

 only 187 millimètres, which lies between the limits of error 

 over such a long distance (7,400 kilomètres). 



Hypsographical Curve of THE Earth's Surface. 



The investigations of modem oceanographers hâve given 

 us a fairly comprehensive knowledge of the nature and extent 

 of the sea bottom, its depth, physical constituents, and animal 

 life. Generally speaking, the great océans are far from shallow, 

 and the volume occupied by water below sea-level greatly 

 exceeds the volume of land above sea-level. If the land above 

 sea-level were tipped into the sea it would only partially dis- 

 place the sea-water (see Fig. 2). 



The greatest oceanic depths far exceed the heights of 

 the highest mountains. Nero Deep, off the island of Guam 

 (Marianne or Ladrone Islands, North Pacific) is 5,270 fathoms 

 or 31,620 feet deep. Mount Everest, the highest mountain in 

 the world, is 29,000 feet high. Nero Deep is, however, an 

 extensive dépression, and an area équivalent to the islands of 

 Sardinia and Sicily lies below 3,830 fathoms. 



The hypsographical curve gives an idea of the relationships 

 of land to water at the earth's surface. It shows us the rela- 

 tively small area of sea bottom within the 200-metre line and 

 below 5,750 mètres. The descent from the continental shelf 

 edge in about 200 mètres to a depth of 3,000 is extremely 

 sharp, and between 1,000 and 3,000 mètres there is only 14-8 



