142 HEAT. 



tions to the expansion of bodies by heat ; a few bodies 

 expand when at a certain temperature, either by an 

 increase or decrease of heat. 



Water is the most singular and important instance of 

 this effect : this liquid decreases in bulk until it has cool- 

 ed to a certain point, and then increases just as if heat 

 were applied. The temperature at which water has the 

 greatest density, is at about 40 of Fahrenheit, at which 

 point it expands either by heat or cold. 



The expansive force of water in the act of freezing, is 

 practically known to almost every person in our climate. 

 Water left in earthen or glass vessels, during cold wea- 

 ther, expands in freezing, and breaks the vessel. Pipes 

 for conducting water are often burst, by water freezing 

 in them. The pavement stones of our streets are often 

 observed during fall and winter to be raised out of their 

 places, which is caused by the freezing of the water be- 

 neath them. The earth around rocks and stones is often 

 observed to be separated from them, which is frequently 

 supposed to arise from the rocks and stones sinking, 

 which, in truth, is caused by the water in the earth, which 

 freezes and expands, while the rock does not expand, 

 but diminishes in a small degree only. Rocks are rent 

 asunder, trees are split by this property of water. This 

 agency of water is a striking instance of the Divine good- 

 ness, in causing rocks and soils to moulder to powder, 

 thereby fitting them well for the purposes of the hus- 

 bandman. 



If it were not for this property of water, our rivers and 

 brooks would in the course of our winters, become en- 

 tirely solid, which of course, would destroy their innu- 

 merable inhabitants ; the seas and oceans of the polar re- 

 gions of the earth woukl become one entire mass of ice, 

 because the ice as soon as formed on the surface, would 

 sink to the bottom, and another layer would be formed, 

 and sink also ; in this way the whole would be frozen. 



The writer of this tract has burst an iron bomb shell, 

 7 inches in diameter and nearly 1 inch thick, by the 

 freezing of water. Some Venetian philosophers burst a 

 brass globe one inch in diameter by freezing water in it, 

 which it was calculated, was equal to a force of 27,720 

 pounds. 



The expansion of water in the act of freezing, is sup- 



