146 THE GREAT ATMOSPHERIC OCEAN. 



think, will, however, increase this estimate: it is not 

 easy to place a limit to the possible tenuity of an 

 elastic gas. 



Be that as it may, however, this atmospheric ocean 

 has its tides, its currents, and its circulation, exactly 

 as has its terrestrial counterpart ; and though of course 

 the specific gravities of the two elements widely differ, 

 air has still its measurable weight, just as water has. 

 Its pressure upon the surface of the sea being, as we 

 all know in these comparatively enlightened days, 

 something like 15 pounds to the square inch: or, to 

 speak more accurately, its weight is equal to 14.7304 

 pounds on each square inch. 



This is not so very much less than that of the 

 steam in the old low pressure boilers of our engines; 

 if, however, we desire to understand what that 

 means, we find a good illustration in the fact that 

 the body of a man of ordinary size sustains a pressure 

 of about fourteen tons. * In consequence, however, 

 of this pressure being equally exerted in every direc- 

 tion, both within and without the body, we sustain it 

 unconsciously, though the addition even of a single 

 pound, placed say upon the hand, is sensibly felt. 

 Such, however, is the Law of Nature: equal forces, 

 exerted in opposite directions, neutralize each other. 



The winds of course represent the currents of the 

 atmospheric sea, this is easily understood ; but as 

 regards its tides the matter is not so clear. Never- 

 theless the subject is one of vast importance. They 

 ebb and flow according to the season, exactly as do 

 the marine tides: high tide being in this case repre- 



* Encyd. Brit., gth edit., Vol. iii, p. 28. 



