EXCEPTION TO EXPANSION BY HEAT. 247 



ice expand ; but if it is often repeated, they are crack- 

 ed into fissures. A strong brass globe, the cavity of 

 which was only one inch in diameter, was used by the 

 Florentine academicians for the purpose of trying the 

 expansive force of freezing water, by which it was 

 burst, although the force required was calculated to be 

 equal to fourteen tons. Experiments were tried at 

 Quebec, in one of which an iron plug, nearly tln-ee 

 pounds in weight, was thrown from a bomb-shell to 

 the distance of 415 feet ; and in another, the shell 

 was burst by the freezing of the water which it con- 

 tained. 



This expansion has a most important influence in 

 the pulverization of soils. The water which exists 

 tlu-ough all their minute portions, by conversion to 

 frost, crowds the particles asunder, and when thawing 

 takes place, the whole mass is more completely mel- 

 lowed than could possibly be effected by the most per- 

 fect instrument. This mellowing is, however, of only 

 short duration, if the ground has not been well drain- 

 ed to prevent its becoming again packed hard by soak- 

 ing with water. 



But this is not the most important result from the 

 expansion of water. Much of the existing order of na- 

 ture and of civilized hfe depends upon this property ; 

 without it the great mass of our lakes and rivers would 

 become converted into solid ice ; for, as soon as the 

 surface became covered, it would sink to the bottom, 

 beyond the reach of the summer's sun, and successive 

 portions being thus added, the great body of all large 

 rivers and lakes would become permanently frozen. 

 But instead of this disastrous consequence, the ice, by 



