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 



65 



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-MEAN RE L HUMIDITY 

 -i^EAN TEMP 

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13 16 19 22 25 

 -^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, Voi 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 



