A HISTORY OF SCIENCE 



the liquefaction struggle was not effected through the 

 use of the principle of evaporating liquids which has 

 just been referred to, but by the application of a quite 

 different principle and its elaboration into a perfectly 

 novel method. This principle is the one established 

 long ago by Joule and Thomson (Lord Kelvin), that 

 compressed gases when allowed to expand freely are 

 lowered in temperature. In this well-known principle 

 the means was at hand greatly to simplify and im- 

 prove the method of liquefaction of gases, only for a 

 long time no one recognized the fact. Finally, how- 

 ever, the idea had occurred to two men almost simul- 

 taneously and quite independently. One of these was 

 Professor Linde, the well-known German experimenter 

 with refrigeration processes; the other, Dr. William 

 Hampson, a young English physician. Each of these 

 men conceived the idea and ultimately elaborated 

 it in practice of accumulating the cooling effect of an 

 expanding gas by allowing the expansion to take place 

 through a small orifice into a chamber in which the 

 coil containing the compressed gas was held. In Dr. 

 Hampson's words : 



"The method consists in directing all the gas im- 

 mediately after its expansion over the coils which con- 

 tain the compressed gas that is on its way to the ex- 

 pansion-point. The cold developed by expansion in 

 the first expanded gas is thus communicated to the on- 

 coming compressed gas, which consequently expands 

 from, and therefore to, a lower temperature than the 

 preceding portion. It communicates in the same way 

 its own intensified cold to the succeeding portion of 



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