30 THE HAKMONIES OF NATURE. 



organic life ; and truly, whoever reflects upon the manner how 

 streams originate, and how their waters are constantly replen- 

 ished, cannot fail to view them with a deeper interest than" that 

 which their mere beauty or utility inspires. To him they are not 

 only the melodious ornaments of the valley, the highways of com- 

 merce, the benefactors of mankind, but the effects of a wonderful 

 co-operation of physical laws, all tending to one common end, 

 and as they rush along he fancies he hears a voice proclaiming 

 the glories of their Maker. 



Similar harmonies strike us when we examine the nature of 

 the various atmospherical precipitations with reference to the 

 requirements of organic life. 



How beautiful is the morning dew, glittering in all the 

 colours of the rainbow ; how it refreshes the thirsty plains ; how 

 the plants raise their drooping heads under the influence 

 of its grateful moisture ! Poets have made it the emblem of 

 purity, but physical science, by revealing to us the simple laws 

 that preside over its formation, has rendered it more beautiful 

 still to the reflecting observer. 



Everybody knows that, when in summer a bottle filled with 

 cold water is brought into a warm room, it soon gets covered 

 with thick dew-drops, which presently trickle down its sides, 

 although it was perfectly dry on entering. Whence does this 

 moisture proceed ? Not from the inside of the bottle, as 

 ignorant people might imagine, but from the surrounding atmo- 

 sphere, in consequence of the capacity of the air to absorb 

 or retain moisture, increasing or diminishing as its temperature 

 grows warmer or colder. 



Thus, when the cold bottle is introduced into the room, the 

 warm sheet of air, which is in immediate contact with its 

 surface, immediately cools, and being no longer able to retain 

 the same quantity of aqueous vapours, is obliged to deposit 

 them on the sides of the vessel. As it cools, its weight also 

 increases, it flows downwards, warmer air takes its place to 

 cool in its turn, and thus there is a perpetual deposition of 

 moisture, until the temperature of the bottle has risen to that 

 of the surrounding atmosphere. 



This familiar example suffices to explain the formation of 

 dew, and of all other atmospherical precipitations, such as 

 rain, hail, or snow, as they all result from the influence of 



