SCIENCE OF THE SEA 



CHAPTER I 

 THE AIR 



BY HUGH ROBERT MILL AND D. WILSON BARKER. 



WHILE the waters of the ocean cover more than two- 

 thirds of the solid surface of the Earth, the atmosphere 

 siirrounds the whole of the globe ; it is the only homo- 

 geneous, unlimited expanse subject to the laws of 

 gravitation and to the influence of radiation, found in 

 the triple structure of lithosphere, hydrosphere, and 

 atmosphere, which constitutes our planet. Over the 

 surface of the land the atmosphere is irregularly dis- 

 tributed ; a great mass of air presses heavily on the 

 low ground, but on the higher plateaux and mountains 

 only a fraction of the atmosphere remains above us, 

 and bears but lightly on the ground. This is due 

 to the fact that air is in the highest degree compressible 

 and elastic, and it is compressed by its own weight to 

 such an extent that half the mass of the atmosphere 

 lies within 18,500 feet of sea-level. As the elevation 

 above the level of the sea increases, the air becomes 

 more and more rare, until, at the height of a few miles, 

 it is in such a state of tenuity that life is impossible. 

 Air or at least some of the gases of which air is com- 

 posed can be traced by observations of the reflection 

 and refraction of light and the flight of meteors to a 



