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larger ones, replace, by the formation of rain, hail or snow, the evapora- 

 tion continually taking place at the earth's surface. At the same time 

 it removes some of the moisture from the atmosphere. Thus the 

 variations in temperature, in addition to supplying us with rain and the 

 beneficial results following it, viz., the purifying of the atmosphere from 

 dust and various gasses, returning to the soil the fertilizing materials 

 expended in the atmosphere, and feeding the springs and rivers, and 

 furnishing the higher lying districts with water ; they also serve to pre- 

 vent the air from being at all times at its dew point. 



As has been mentioned water has a great power to act as an 

 equalizer of climate. By its evaporation during the day it has a power- 

 fully cooling influence. This is easily observed when comparing the 

 refreshing coolness of a lawn, which is largely due to the moisture 

 evaporated by the grass, with bare streets and sa.idy jjlains. In addi- 

 tion to this cooling influence, which is the greater the warmer the day, 

 vapour has a tendency to preserve the heat during the night, as it acts 

 as a mantle or blanket to the earth, preventing the too rapid radiation 

 of the heat absorbed during the day. The rapidity with which the 

 thermometer drops durmg a clear star-light night, when the vapour has 

 been partially deposited as snow or rain or drifted by the winds to other 

 parts of the globe, is frequently observed when compared with what 

 takes place on cloudy nights. 



But the water, as such, acts also as an equalizer of temperature. We 

 find that some materials do not increase in temperature as rapidly as 

 others when exposed to the same source of heat ; i.e., some do not vary 

 as easily as others, notwithstanding that they may absorb the same 

 quantity of heat. This is easily seen when comparing the rapidity of 

 increase in temperature of dry sand with that which has been previously 

 moistened; or water with iron or some other metal when exposed to the 

 heat of the sun. The metal and the dry sand become warm much 

 more quickly than the wet sand or the water. Yet, making allowance 

 for the evaporation of water and the quantity of heat reflected from 

 them, the water, though very much colder, will have absorbed the same 

 fjuantity of heat as the other materials and can again transmit it to 

 cooler bodies. Thus during the day, more especially during the sum- 

 mer months, it absorbs the heat of the sun and liberates it again at 



