LOW-TEMPERATURE RESEARCHES 



apparently interfered with by the waves of radiant 

 heat; or, again, that magnetism is presumably due to 

 molecular motions which are apparently interfered 

 with by another kind of molecular motions which we 

 call heat vibrations ; but there is a vagueness about the 

 terms of such guesses that leaves them clearly within 

 the category of explanations that do not explain. 



When it comes to the phenomena of light, we can, 

 as is fitting, see our way a little more clearly, since, 

 thanks to Thomas Young and his successors, we know 

 pretty definitely what light really is. So when we 

 learn that many substances change their color utterly 

 at low temperatures red things becoming yellow and 

 yellow things white, for example we can step easily 

 and surely to at least a partial explanation. We know 

 that the color of any object depends simply upon the 

 particular ether waves of the spectrum which that 

 particular substance absorbs; and it does not seem 

 anomalous that molecules packed close together at 

 i 80 of temperature should treat the ether waves 

 differently than when relatively wide apart at an 

 ordinary temperature. Yet, after all, that may not be 

 the clew to the explanation. The packing of the mole- 

 cules may have nothing to do with it. The real ex- 

 planation may lie in the change of the ether waves 

 sent out by the vibrating molecule; indeed, the fact 

 that the waves of radiant heat and those of light differ 

 only in amplitude lends color to this latter supposition. 

 So the explanation of the changed color of the coaled 

 substance is at best a dubious one. 



Another interesting light phenomenon is found in 

 the observed fact that very many substances become 



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