438 THE CHEMISTRY OF CREATION. 



heat, applied to the surface, produces little 

 or no movement in the particles of water, 

 the application of cold, on the contrary, is a 

 constant cause of motion. In the air, heat 

 causes the particles to ascend; in the water, 

 cold causes the particles to descend. Direct 

 observations are still required on this subject, 

 but it appears probable that this class of move- 

 ments takes place most actively in regions of 

 moderate temperature. Near the equator, 

 during the day the upper stratum of water 

 becomes greatly heated by the sun's rays, but 

 very little disturbance of its particles is thus 

 produced. Again, in the colder regions about 

 the poles, the surface of the water is covered 

 with a dense and solid stratum of ice, or the 

 water when not frozen is scarcely ever higher 

 than 40, at which point its particles lose their 

 tendency to sink ; and here movement is of 

 course arrested. In temperate regions, there- 

 fore, while the nights are very cold, although 

 not so cold as to reduce the temperature to 40, 

 this movement goes on most actively. The sur- 

 face particles constantly losing heat, and so 

 becoming specifically heavier than the particles 

 beneath, sink ; while their place is supplied with 

 warmer particles from below. Thus there is a 

 constant ascent of heated particles, and descent 

 of colder ones, producing, although it is not 



