1912.] 



PUBLIC DOCUMENT — No. 31. 



113 



the humidity is low the cracks show a tendency to open, and to 

 close when the humidity is great. The rise and fall of the 



95 



90 



75 

 70 

 65 



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J 



rin 



n. 



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\ I \ \ I- 



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nil 



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10' 

 0' 



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n 



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u 



30.0 i- 

 29.5 



29.0 m, 



35 

 50 

 25 



zo 



15 

 10 

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u 



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-MEAN REL HUMIDITY 

 -i^EAN TEMP 

 -BAROMETER 

 -FROST CRACK 



7 (0 15 16 19 22 25 28 

 ---. FEB..-''^ 



Showing curve of opening and closing of frost cracks in elm trees. The lower curve repre- 

 sents the variations in the opening and closing (scale, Vm of an inch) ; the others repre- 

 sent the mean relative humidity, mean temperature and barometer in the order named. 



barometer curve coincides very closely with that of the frost 

 cracks ; in fact, there was such a close relationship between the 

 temperature and barometer readings and opening and closing 



