42 



HYDROLOGY 



measurement, when the molecular constitution of a body is being 

 changed. 



Specific Heat. The specific heat of water is greater than all 

 known substances with the exception of bromine and hydrogen, 

 and it is the basis for measurement of the capacity of heat absorp- 

 tion of all other substances. Its value varies with the tempera- 

 ture of the water, being lowest near 40 C., after which it increases 

 up to and beyond the boiling-point. The generally accepted 

 values as determined by Peabody are given in Table XVIII. 



TABLE XVIII 



SPECIFIC HEAT OF WATER AT VARIOUS TEMPERATURES 



Effect of Atmospheric Pressure. At sea level the average 

 atmospheric pressure is 14.72 pounds per square inch, but it 

 decreases as the height above sea level increases. With water 

 weighing 62.4 pounds per cubic foot, the weight of a column having 



