10 BERTHA'S VISIT TO HER 



was dewed ; and the thermometer being applied 

 to each, the heat of the depressed one was found 

 to be 56, while the other was only 49 ; for not 

 only had the upper glass more readily parted 

 with its heat by radiation, but the other had re- 

 ceived a constant supply of heat from the sur- 

 rounding earth. In the same manner it may be 

 explained, why the prominent parts of bodies are 

 often encrusted with hoar frost, while the more 

 solid and retired parts are free from it." 



I then inquired, why there is less dew of a 

 windy evening; for one would suppose, that 

 wind, instead of preventing the radiation of heat, 

 would rather help to promote it. 



He replied, " all bodies exposed in a clear 

 night must undoubtedly radiate as much of their 

 heat during a storm as in the most perfect calm ; 

 but, whenever radiation is going on, the air 

 is more or less warmed by it ; and consequently 

 wind, which is only air in motion, serves to bring 

 a continual stream of its warm particles into 

 contact with those bodies. This restores almost 

 as much heat as they had lost, and prevents 

 the deposition of dew ; for, you know, dew is 

 nothing but the moisture of the atmosphere con- 

 densed by meeting with colder substances; and, 

 therefore, whatever tends to equalize the tem- 

 perature of the air, and of those substances, must 

 obstruct the formation of dew." 



We breakfasted at Kidderminster, and saw 



