THERMOMETRICAL TABLES. Xlii 



Conversion of differences Fahrenheit to differences Centigrade. Table 5. 



The table gives for everj^ tenth of a degree from o° to 2o°9 F. the 

 corresponding lengths of the Centigrade scale. 



Conversion of differences Centigrade to differences Fahrenheit. Table 6. 



The table gives for every tenth of a degree from o° to g°.g C. the corre- 

 sponding lengths of the Fahrenheit scale. 



Example : 



To find the equivalent difference in Fahrenheit degrees for a difference 



of 4f72 Centigrade. 

 From the table, 4^70 C. = 8r46 F. 



From the table by moving the decimal point for 0.2, 0,02 = 0.04 



4^72 C. = 8^50 F. 



REDUCTION OF TEMPERATURE TO SEA LEVEL. 



English Measures. Table 7. 



Metric Measures. Table 8. 



These tables give for different altitudes and for different uniform rates 

 of decrease of temperature with altitude, the amount in hundredths of a 

 degree Fahrenheit and Centigrade, which must be added to observed tem- 

 peratures in order to reduce them to sea level. 



The rate of decrease of temperature with altitude varies from one 

 region to another, and in the same region varies according to the season 

 and the meteorological conditions ; being in general greater in w'arm lati- 

 tudes than in cold ones, greater in summer than in winter, and greater 

 in cyclones than in anti-cyclones. For continental plateau regions, the 

 reduction often becomes fictitious or illusory. The use of the tables there- 

 fore requires experience and judgment in selecting the rate of decrease 

 of temperature to be used. 



The tables are given in order to facilitate the reduction of temperature 

 either upwards or downwards in special investigations, but the reduction is 

 not ordinarily applied to meteorological observations. 



The tables, 7 and 8, are computed for rates of temperature change 

 ranging from 1° Fahrenheit in 200 feet to 1° Fahrenheit in 900 feet, and 

 from 1° Centigrade in 100 metres to 1° Centigrade in 500 metres; and 

 for altitudes up to 5,000 feet and 3,000 metres respectively. 



Example, Table 7 : 



Obser\^ed temperature at an elevation of 2,500 feet, 52°5 /\ 



Reduction to sea level for an assumed decrease in tem- 

 perature of \°F. for every 300 feet, -f 8.°3 



Temperature reduced to sea level, 6o.°8 F. 



