SECTION II. 

 METEOROLOGY. 



METEOROLOGY has been defined as the " Science of the Weather 

 and Climate," and thus includes the varied phenomena taking place 

 in the atmosphere. In what follows will be found a description of 

 the chief phenomena investigated and the means by which this 

 investigation is carried out. 



TEMPERATURE is measured by means of a thermometer. The 

 common type of thermometer is one in which mercury or alcohol 

 is used as the thermometric substance, the measurement depending 

 upon the thermal expansion of the substance. Alcohol thermo- 

 meters can be used for recording lower temperatures than mercury 

 ones, since the freezing point of alcohol is -130 C, while that of 

 mercury is -39 C. 



The thermometer is graduated and divided into degrees. There 

 are two fixed points, viz., the temperature of steam rising from 

 water boiling under standard pressure (760 mm. of mercury) and 

 the temperature of melting ice. These points are indicated respect- 

 ively by 212 and 32 on the Fahrenheit scale, the interval between 

 them being divided into 180 equal parts or degrees. The corres- 

 ponding points and interval in the case of the Centigrade scale are 

 100 and with 100 degrees between, while for the Reaumur 

 scale they are 80 and with 80 degrees between. To convert 

 from one scale to another : if F, C, R represent the same temper- 

 ature on Fahrenheit, Centigrade and Reaumur scales respectively, 

 then the following relation can be used for the required 



conversion: = = e.g., to convert ioC to Fahrenheit, 



180 100 80' 



^= = .'. F-32=i8 . F = 50 Fahrenheit. 

 180 100 loo 



There is another scale called the Absolute Scale, the zero of 

 which is -273 C, so that if A be the absolute temperature and C 

 the Centigrade, the relation is A = 



37 



