TEMPERATURE 67 



increases and the density diminishes with 

 a rise of temperature, but also below this 

 temperature the volume increases and the 

 density diminishes with a fall of temperature. 

 On freezing at 32° F., the ice, unlike most 

 other substances, occupies a larger volume 

 than an equal weight of water. 



The specific heat of sea-water is less 

 than that of fresh water, and sea- water is a 

 better conductor of heat than fresh water. 

 Again, the freezing point and the maximum 

 density point of sea-water depend on the 

 salinity. Water with a salinity of 35 per 

 thousand freezes at 28° F., and the maximum 

 density point is at the freezing point. It 

 follows that any sea-water on being cooled 

 will always sink through water of equal 

 salinity, while fresh water at a temperature of 

 39. 2° F. will always sink through water having 

 either a higher or a lower temperature. 



In all questions dealing with the circulation 

 of fresh water in lakes and of salt water in 

 the ocean it is most important to bear these 

 fundamental facts in mind. They account 

 for the marked differences in the distribution 

 of temperature in fresh- water lakes and in the 

 ocean. 



The methods and instruments employed in 

 observing the temperature of ocean waters 

 both at the surface and in great depths, have 



