126 



TABLE IX. 



FACTOR -, FOR COMPUTING THE RELATIVE HUMIDITY, OR THE DEGREE OF MOISTURE 



OF THE AIR, EXPRESSED IN HUNDREDTHS, FROM ITS ABSOLUTE 



HUMIDITY GIVEN IN ENGLISH MEASURES. 



THE Relative Humidity, or the degree of moisture of the air, is, as explained 

 above, the ratio of the quantity of vapor contained in the air to the quantity it could 

 contain at the temperature observed, if fully saturated. 

 If we call 



The force of vapor contained in the air = jf, 



The maximum of the force of vapor at the temperature of the air = F, 



The point of saturation = 100, 



we have the proportion, 



Relative Humidity : 100 : :/: F, 

 and 



^100 = Relative Humidity in Hundredths. 



But as f-l~Q =f x -jr, it is obvious that the operation indicated by the former 



expression, viz. jr-, would be reduced to a simple multiplication, if we had a 

 table of the factors . Such a table is obtained by dividing the constant number 

 100 by each number in the Table of Elastic Forces of Vapor, and substituting the 

 quotients for the tensions, or forces of vapor. 



The following Table gives the factor ^ for every tenth of a degree from to 

 104 Fahrenheit, corresponding to the Forces of Vapor in Table VI., or Regriault's 

 table reduced to English measures. 



USE OF THE TABLE. 



The force of vapor contained in the air, or its absolute humidity, being given in 

 English measures, multiply the number expressing it by the factor in the table cor- 

 responding to the temperature of the air at the time of the observation ; the result 

 will be the Relative Humidity in Hundredths. 



Examples. 

 1. Suppose the temperature of the air to be = 60 Fahrenheit. 



" " force of vapor in the air to be = .388 English inch. 



Opposite 60 is found in the table the factor 193.1. 



Then 0.388 X 193.1 = 74.9, Relative Humidity in Hundredths. 



2. Suppose the temperature of the air to be = 74. 5 Fahrenheit. 

 " " force of vapor in the air to be'= .650 English inch. 

 Table gives for 74.5 the factor 117.2. 



Then 0.650 X 117.2 = 76.2, Relative Humidity required. 



B 90 



