THE EEASON WHY. 161 



1 For so the Lord said unto me, I will take my rest, and I will consider in my 



dwelling place like a clear heat upon herbs, and like a cloud of dew 



in the heat of harvest." ISAIAH xvm. 



Fair weather indicated by the rise of the mercury. 



Foul weatlier by the fall of the mercury. 



Thunder, indicated by the fall of th<> mercury in sultry weather. 



Cold, indicated by the rise of the mercury in spring, autumn, and winter. 



Heat, by ihefall of the mercury in summer and autumn. 



Frost, indicated by the rise of the mercury in winter. 



Thaw, by the fall of the mercury during a frost. 



Continued bad weather, when the fall of the mercury has been gradual 

 through several fine days. 



Continued fine weather, when the rise of the mercury has been gradual 

 through several foui days. 



Bad weather of short duration, when it sets in quickly. 



Fine weather of short duration, when it sets in quickly. 



Changeable weather, when an extreme change has suddenly set in. 



Wind, indicated by a rapid rise or fall unattended by acliange of temperature. 



The mercury rising, and the air becoming cooler, promises fine weather ; but 

 the mercury rising, and the air becoming warmer, the weather will be 

 changeable. 



If the top of the column of mercury appears convex, or curved upwards, it is 

 an additional proof that the mercury is rising. Expect fine weather. 



If the top of the column is concave, or curved downwards, it is an additional 

 proof that the mercury is falling. Expect bad weather. 



CHAPTER XXXIII 



709. What is the thermometer ? 



The thermometer is an instrument in which mercury is employed 

 to indicate degrees of heat. Its name is derived from two Greek 

 words, meaning heat measurer. 



710. Why does mercury indicate degrees of heat? 



Because it expands readily with heat, and contracts with cold ; 

 and as it passes freely through small tubes, it is the most convenient 

 medium for indicating changes of temperature. 



711. Why are there Reaumur's Thermometers and Fahren- 

 heit's Thermometers ? 



Because their inventors, after whom they are named, adopted a 

 different system of notation, or thermometrical marlcs ; and as 

 their thermometers have been adopted by various countries and 

 authors, it is now diLcw.. 1 dispense with either of them. 



