THE CONDENSER. 



429 



popularly known as the " Low-pressure Engine." In this 

 case force is reconverted, so to speak, and, if a cubic inch of 

 water has been converted by heat into a cubic foot of steam, 

 creating a pressure in one direction, it can be reconverted by 

 cold, and so produce a pressure in another direction. 



It is owing to this fact that some parts of the world are 

 always hot and always wet, Guiana being a striking example. 



The wind blows over the ocean, absorbing moisture as a 

 sponge does water. As it passes from the sea over the land, it 

 is met by secondary mountain ranges, too low to arrest its pro- 



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3 



RAIN-CLOUD. 



CON DENSER. 



gress altogether, and high enough to have their summits clothed 

 in eternal snows. As soon, therefore, as the warm, water-laden 

 winds pass over these mountains, the moisture is condensed by 

 their frozen tips, and down rushes the rain in torrents. 



Even in our own temperate land we can often trace the 

 cause of a heavy rain to the presence of a lofty hill, or even an 

 exceptionally tall spire. The moist climate of Oxford has been 

 attributed by scientific men quite as much to its spires and 

 towers as to its low-lving situation. 



Now we come to the various modes of extracting the water 

 which is laid up within the earth, and which only slowly 

 ascends to the surface when drawn up by the heat of the sun. 



Water is everywhere, but the depths at which it is found are 

 vastly different. For example, at one house in which I lived 

 it was not possible to dig for three feet without coming to 

 water. In another, no water was found within some two 

 hundred feet, and, as I several times relieved the old gardener 

 of the task of drawing the water for the day's consumption, I 

 have reason to remember the depth. 



