THE IMPENETRABLE SEA 



orange. But the comparison fails if we imagine the tiny 

 irregularities on the skin of an orange as representing the 

 mountains, valleys and ocean beds of our world. Even the 

 smoothest-skinned orange would be too coarsely surfaced 

 to represent them — an orange-sized ball with an appar- 

 ently smooth surface would be a better representation. 



The earth's diameter is nearly 8,000 miles. Compare it 

 with the heights of the world's loftiest mountains, and 

 the deepest depths of its oceans. Twenty mountain peaks 

 are over 20,000 feet in height. Of these the highest is 

 Everest — 29,028 feet. One of the deepest spots in the 

 oceans was discovered south-west of Guam in 1951 by 

 the British survey ship Challenger — named after the 

 famous oceanographic vessel that circled the globe in 

 1872-76. Known as the Challenger Depth, this is six and 

 four-fifths miles down into the earth, and might seem to 

 be more than a scarcely-visible prick in the skin of an 

 orange. But even if we increase the Challenger Depth a 

 little, calling it, for convenience's sake, seven miles, it is 

 still less than a thousandth of the diameter of the earth. 



There can be little doubt that human beings will one 

 day descend to the deepest points in the world's oceans — 

 probably exploring chasms many hundreds of feet deeper 

 than those known to us at present. But enough explora- 

 tion has already taken place to give us a rough idea of 

 the downward limit of ocean penetration. We can accept 

 seven miles as a reasonable figure. But the average depth 

 of the world's oceans has been calculated at very con- 

 siderably less than this : 14,200 feet, or roughly 2f miles. 

 Some authorities make it somewhat less. 



All man's normal activities take place within the 

 twelve and a half miles range indicated : that is, in the 

 superficial ''thickness" lying between the top of Everest 

 and the lowest depth in the ocean. The use of the word 

 "normal" is essential in this age, for men occasion- 

 ally pass upward, far above Everest, making their alti- 

 tude records, such exploits being exceptions, however, to 



22 



