208 BERTHA'S VISIT TO HER 



that about an hour before sun-rise the dew 

 was particularly abundant. The window was 

 frequently kept a little open at night, when the 

 room was close, and the weather still ; but 

 the air became so chilly just as this heavy 

 dew came en, that she was always obliged 

 to shut it ; yet during the night the chill was 

 never perceived ; which corroborates what Dr. 

 Wells says, " that the cold of the atmosphere 

 is greater in the latter than the prior part of the 

 night." 



In the course of Dr. Wells' observations, he 

 found that dew does not form readily on gravel- 

 walks ; and that if the atmosphere be clear, 

 neither the road or pavement are moistened with 

 dew, though the grass on the road side, and 

 painted doors and windows, are frequently wet. 

 He found also, that wool, though highly attrac- 

 tive of dew, was prevented, if placed on a 

 gravel-walk, from acquiring as much dew as an 

 equal parcel of wool, if laid upon grass. 



I asked why Dr. Wells used wool in these 

 experiments, and my uncle told me, that at first 

 he had only compared the quantities of dew on 

 bodies having smooth surfaces ; but that he 

 found wool much better adapted to collect dew 

 from the atmosphere, as it readily admits the 

 moisture amongst its fibres, and retains what it 

 receives very firmly. Filamentous and downy 

 substances are by far the most productive of 



