PHYSICAL PARADOXES. 



another pipe, and forces it through a third 

 pipe into the boiler. Briefly, steam from the 

 boiler, and getting its pressure from the boiler, 

 overcomes the pressure of the steam still in 

 the boiler, and re-enters the boiler, carrying 

 fresh water in with it. 



This sounds a paradox indeed. Yet the 

 wonder is still greater, for exhaust steam will 

 do this. Steam which has passed through the 

 engine, done its work there, and so been reduced 

 to atmospheric pressure, will overcome a boiler- 

 pressure of, say, four atmospheres, and carry 

 in water with it, raising or pumping this water, 

 moreover, from a lower level. 



This contradictory state of things depends 

 upon the sudden condensation of the steam, 

 concentrating all its energy within a very small 

 volume. 



When a jet of steam issues into a space 

 where the pressure is about half of that in the 

 steam chamber, it moves at a speed of fourteen 

 or fifteen hundred feet per second, which 

 becomes higher still after the steam has ex- 

 panded. Moving at this velocity, particles have 

 a great deal of moving energy, though they be 

 small and light, like the particles of steam. 



Now, steam occupies at atmospheric pres- 

 sure more than seventeen hundred times the 

 volume that it occupied as water. 



If, therefore, it is condensed or turned into 

 water again, it goes back into less than the 



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