WATER 



sinks to the bottom. We can feel this for our- 

 selves if we lie in a warm bath and do not stir 

 up the water. A layer of cooler water will 

 begin to form at the bottom, while the warm 

 water rises to the top, and uses up some of its 

 heat in doing the work necessary to separate 

 some of its particles and send them away into 

 the air as vapour. All the time it is cooling 

 the water contracts, its particles become closer 

 together, which, as in the case of the air, or the 

 box of bricks, makes it heavier. Just before it 

 reaches the freezing point the process alters, and 

 it actually begins to expand and spread itself 

 out, as though the particles were re-arranging 

 themselves in some way, ready to form the 

 crystalline solid we call ice, and required rather 

 more room to settle into their new places. So 

 the water, which is nearly frozen, begins to rise 

 again, and its place at the bottom is taken by 

 water which is almost but not quite as cold, and 

 when the ice is actually formed, we find it float- 

 ing on the top of the water. 



This is certainly a most wonderful provision 

 of Nature. Let us think what some of the 

 results would be if the ice were to sink to the 

 bottom. Layer upon layer of ice would form 

 and sink down until the ponds and rivers became 

 a solid mass of ice, through which no fish could 

 move, in which all animal and vegetable life 

 would be suspended or destroyed. Then, when 

 the warm weather came, the surface of the water 



(29) 



