106 THE FITNESS OF THE ENVIRONMENT 



c 



THERMAL CONDUCTIVITY 



The heat conduction of water is also a maxi- 

 mum among ordinary liquids, and, though 

 very low compared with good conductors like 

 metals, must favor the equalization of tempera- 

 ture within the living cells whose structure hin- 

 ders the establishment of convection currents. 



Table of Heat Conductivities 



Water 0.0125 Rubber 0.0004 



Alcohol 0.00048 Tin 0.15 



Ether 0.00034 Lead 0.08 



Benzene 0.00033 Iron 0.16 



Glycerine 0.00066 Copper 0.72 



Crown glass .... 0.0016 Silver 1.10 



D 



EXPANSION BEFORE FREEZING 



A final thermal property of water remains 

 to be considered; namely, its anomalous ex- 

 pansion when cooled at temperatures near 

 the freezing point. The facts are illustrated 

 by the accompanying table. 



evaporation, and the rate of evaporation of water. It will 

 be seen that eighty years ago it was already possible to 

 make out a strong case for the fitness of water ; but it should 

 not be forgotten that at that time ideas were in some respects 

 still very vague, and comparative data few. 



