366 PLEASANT WA YS IN SCIENCE. 



bourhood might otherwise tend to check the loss of heat in 

 objects on the ground. 



Here, also, we recognize the cause of the second pecu- 

 liarity detected by Aristotle namely, that dew is only 

 formed copiously in serene weather. When there is wind, 

 it is impossible that the refrigerated air around an object 

 which is parting with its radiant heat, can remain long in 

 contact with the object Fresh air is continually supplying 

 the place of the refrigerated air, and thus the object is pre- 

 vented from growing so cold as it otherwise would. 



In conclusion, we should wish to point out the important 

 preservative influence exercised during the formation of dew. 

 If the heat which is radiated from the earth, or from objects 

 upon it, during a clear night, were not repaired in any way. 

 the most serious injury would result to vegetation. For 

 instance, if the sun raised no vapour during the day, so that 

 when night came on the air was perfectly dry, and thus the 

 radiant heat passed away into celestial space without com- 

 pensation, not a single form of vegetation could retain its 

 life during the bitter cold which would result But consider 

 what happens. The sun's heat, which has been partly used 

 up during the day in supplying the air with aqueous vapour, 

 is gradually given out as this vapour returns to the form 

 of water. Thus the process of refrigeration is effectually 

 checked, and vegetation is saved from destruction. There 

 is something very beautiful in this. During the day, the 

 sun seems to pour forth his heat with reckless profusion, 

 yet all the while it is being silently stored up ; during the 

 night, again, the earth seems to be radiating her heat too 

 rapidly into space, yet all the while a process is going on by 

 which the loss of heat is adequately compensated. Every 

 particle of dew which we brush from the blades of grass, as 

 we take our morning rambles, is an evidence of the preser 

 vative action of nature. 



