LOW-TEMPERATURE RESEARCHES 



high temperature, is one of the standing puzzles of 

 physics. And the demonstrated increase of this ca- 

 pacity at very low temperatures only adds to the mys- 

 tery. 



There are at least two of the low-temperature phe- 

 nomena, however, that seem a little less puzzling the 

 facts, namely, that cohesion and rigidity of structure 

 are increased when a substance is cooled and that 

 chemical activity is very greatly reduced, in fact al- 

 most abolished. This is quite what one would expect 

 a priori though no wise man would dwell on his ex- 

 pectation in advance of the experiments since the 

 whole question of liquids and solids versus gases ap- 

 pears to be simply a contest between cohesive forces 

 that are tending to draw the molecules together and 

 the heat vibration which is tending to throw them 

 apart. As a substance changes from gas to liquid, and 

 from liquid to solid, contracting meantime, simply 

 through the lessening of the heat vibrations of its 

 molecules, we might naturally expect that the solid 

 would become more and more tenacious in structure 

 as its molecules came closer and closer together, and 

 at the same time became less and less active, as hap- 

 pens when the solid is further cooled. And for once 

 experiment justifies the expectation. Professor De- 

 war found that the breaking stress of an iron wire is 

 more than doubled when the wire is cooled to the tem- 

 perature of liquid air, and all other metals are largely 

 strengthened, though none other to quite the same 

 degree. He found that a spiral spring of fusible metal, 

 which at ordinary temperature was quickly drawn out 

 into a straight wire by a weight of one ounce, would, 



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