CHAPTER XYIIL 



LIQUID AIR. 



Air, like water, assumes the liquid form at 

 a certain temperature. Water boils and 

 vaporizes at 212 degrees Fahrenheit above 

 zero, while liquid air boils and vaporizes at 

 312 degrees below zero. 



Heat and cold are practically relative terms, 

 although scientists talk about an "absolute 

 zero " (the point of no heat), and Professor 

 Dewar fixes this point at 461 degrees Fahren- 

 heit below zero. Others have estimated that 

 the force of the moon during its long night of 

 half a month, is reduced in temperature to six 

 or seven hundred degrees below, which is far 

 lower than Professor Dewar's absolute zero. 

 However this may be, to an animal that is de- 

 signed to live in a temperature of 70 or 80 

 degrees Fahrenheit, any temperature below 

 zero would seem very cold. If, however, we 

 were adapted to a climate where the normal 

 temperature was 312 degrees Fahrenheit below 

 zero, we should be severely burned if we should 

 sit down upon a cake of ice. Such a climate 



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