CHAPTER III. 



RAIN AND DEW. 



In travelling by steamer, it often happens that on going to 

 that side of the boat towards which the wind is blowing 

 the passenger suddenly finds himself in a shower of fine 

 rain. This artificial shower is produced by the steam which 

 issues from the waste-pipe being cooled down by contact 

 with the surrounding cold air until it is condensed in the 

 shape of drops of liquid. Every natural shower of rain 

 is produced by a process of condensation similar to this, 

 but carried on in the higher regions of the atmosphere. 



It is instructive to observe the dense clouds of steam 

 which roll forth from the spout of a kettle of boiling water, 

 or from the escape-pipe of a steam-engine. In most cases, 

 nothing can be seen close to the point from which the 

 vapour issues, and it is only at some distance from this 

 point that the white clouds first make their appearance. 

 But, since that intervening space lies directly in the path 

 of the issuing vapour, it is clear that it must be traversed 

 by steam, though the eye fails to detect it. In fact, the 

 steam, or watery vapour, when pure and uncondensed, is 

 as transparent, as colourless, and as invisible as the air 

 we breathe or the gas we burn. It is only when the vapour 



