80 ROYAL SOCIETY OF CANADA 



inution will go oni till the temperature falls from 3 to 3, from 2 to 1^ 

 and from 1 to zero. To conclude, water has a maximum of density, 

 which does not coincide with its term of congelation. At 4° above 

 zero is the maximum of density. 



There is nothing so simple as to point out in what manner the 

 congelation of stagnant water takes place. 



Let us suppose, as is always the case, that at the moment when 

 the wind blowing from the north produces ice, the water throughout 

 to be at +10°. The cooling of the liquid, by coming in contact with 

 the glacial air, will be affected from the exterior to the interior. The 

 surface which, hypothetically speaking, was at 10° will soon be at 9° ; 

 but at 9° the water will possess more density that at 10°; then, in 

 consequence of the principle of hydrostatics formerly mentioned, it 

 will sink to the bottom of the mass, and be replaced by a layer not 

 yet cooled, whose temperature is 10°. That, in its turn, will be 

 affected like the first layer, and so on of the rest. In a greater or 

 less time the whole mass will then be at +9°. 



Water at -|-9° will become cool in the same way as at 10° by 

 consecutive layers. Each in its turn, on coming to the surface, will 

 lose one degree of temperature. The same phenomenon will reappear, 

 with similar circumstances, at 8°, 7°, 6°, and 5° ; but, on sinking 

 to 4°, every thing will be changed. 



At +4° (39°. 2 Fahr.) water will actually reach its maximum 

 of density. Should the action of the atmosphere take away a degree 

 of heat from the superficial layer, or descend to 3°, the layer will be 

 less dense than the portion of fluid which it covers; it will never sink 

 into it. An additional diminution in the heat will not cause it to 

 sink more, as water at -\-2° is lighter than at +3°, etc. 



It is quite obvious, however, that the layer in question, by remain- 

 ing always on the surface, incessantly exposed to the cooling influence 

 of the atmosphere, will at length lose the first 4° of its heat. It will 

 end by falling to zero, and freezing. 



The superficial sheet of ice, however singular the phenomenon may 

 be, is then found resting on a liquid mass, whose temperature, at least 

 at the bottom, is 4° above zero. 



The congelation of stagnant water could not evidently take place- 

 in any other manner. I repeat, that no person has ever seen the 

 formation of ice beginning at the bottom of a lake or pond. 



Let us briefly examine the modifications which the motion of the 

 liquid should produce. 



The effect of this motion, when it is rather rapid, when it forms 

 eddies, and flows over a rocky or unequal channel, is perpetually t» 



