#02 PHYSICAL NATURE OF WATER. 



therefore, seek to explain the action of the formation 

 of ice, as we know it, by some more rational view. 



Water expands by heat, and contracts by cold ; con- 

 sequently, the coldest portions of this body occupy the 

 lower portions of the fluid ; but it must be remembered 

 that these parts are warmed by the earth. Ross, how- 

 ever, states that at the depth of 1,000 fathoms the sea 

 has a constant temperature of 39. Water is said to be 

 at its point of greatest density at 40 of Fahrenheit's 

 thermometer; in cooling further, this fluid appears to 

 expand, in the same way as if heated : and, consequently, 

 water colder than this point, instead of being heavier, is 

 lighter, and floats on the surface of the warmer fluid. 

 It does not seem that any modification of the law is re- 

 quired to account for this phenomenon. Water cooled 

 to 40 still retains its peculiar corpuscular arrangement ; 

 but immediately it passes below that temperature, it 

 begins to dispose itself in such a manner that visible 

 crystals may form the moment it reaches 32. Now, if 

 we conceive the particles of water, at 39, to arrange 

 themselves in the manner necessary for the assumption 

 of the solid form, by the particular grouping of mole- 

 cules in an angular instead of a spheroidal shape, it will 

 be clear, from what we know of the arrangement of 

 crystals of water ice that they must occupy a larger 

 space than when the particles are disposed, side by 

 side, in minute spheres. Even the escape of air from 

 the water in which it is dissolved is sufficient to give an 

 apparent lightness to the colder water. This expansion 

 still goes on increasing, from the same cause, during the 

 formation of ice, so that the specific gravity of a mass of 

 frozen water is less than that of water at any tempera- 

 ture below 40. It must not be forgotten that ice 

 always contains a large quantity of air, by which it is 

 rendered buoyant. 



Water, at rest, may be cooled many degrees below 

 the freezing point without becoming solid. This is 



