THE WEATHER, AND WEATHER PROPHETS. 159 



(22.) When water is converted into invisible vapour, 

 it occupies between sixteen and seventeen hundred 

 times its original volume, and becomes much lighter 

 than air as light, indeed, as the ordinary coal gas with 

 which balloons are filled, so that if enclosed in a similar 

 envelope it would rise in the air like a balloon. Being 

 free, however, it mixes with the air, and that not merely 

 by a simple chance-medley confusion, but by a peculiar 

 self-diffusive energy arising from its inherent elasticity; 

 by which the particles of every one species of gas or 

 vapour struggle to interpenetrate, and needle, as it were, 

 their way among those of every other. These latter oppose 

 to them no elastic pressure, but that simple resistance to 

 jostling which an inert body of any other kind might do, 

 which feathers, for instance, might oppose to air, in- 

 troduced and struggling to diffuse itself among them. 

 Of course they will be pushed from their places in the 

 struggle, both laterally and vertically, and thus arises 

 over the whole region in which the vapour is in course 

 of production, a pressure on the air both outwards and 

 upwards. The former, however, cannot be effective in 

 removing air bodily to any great distance horizontally, 

 for the simple reason that to do so it would have to 

 shove aside the whole surrounding aerial atmosphere, and 

 to crowd it upon that which is beyond : while there is 

 room in a vertical direction for an indefinite removal, 

 and the upward pressure is also aided by the lightness of 

 the up-struggling vapour, which therefore rises rapidly 

 not without dragging up with it a great deal of air. The 

 consequence is to establish, immediately under the sun, 



