108 THE FITNESS OF THE ENVIRONMENT 



steadily contracted on cooling, so that its 

 point of maximum density fell at the freezing 

 point, it is impossible to say how great would 

 be the disadvantage for living organisms. 

 Certain it is that life upon the earth would be 

 thereby very greatly restricted. For this prop- 

 erty, together with the by no means unique phe- 

 nomenon of expansion upon solidification, 1 is 

 very largely responsible for the permanence 

 in liquid state of many bodies of water in 

 cold climates. In salt water the anomalous 

 contraction disappears, and the lack of paleo- 

 crystic ice is due to the density of ice and to 

 the great mass of the ocean and the movement 

 of its waters. 2 



There is an old experiment of Rumford's 

 which well illustrates what conditions must 

 have been had the contraction of water been 

 normal and ice denser than water. 3 He 

 found that in a vessel filled with water, which 

 contains ice confined at the bottom, it is 

 possible to heat and even boil the superficial 

 portion of the water without melting the ice. 

 And so it would be with lakes, streams, and 

 oceans were it not for the anomaly and the 



1 The density of ice at the melting point is 0.91674. 



2 A full discussion of this subject will be found in S. 

 Giinther's "Handbuch der Geophysik." 



3 See Whewell's Bridgewater Treatise. 



