72 



TABLE IV. 



FACTOR p^, FOR COMPUTING THE RELATIVE HUMIDITY, OR THE DEGREE OF MOISTURE 

 OF THE AIR FROM ITS ABSOLUTE HUMIDITY, GIVEN IN MILLIMETRES. 



By HAEGHENS. 



The Relative Humidity, or the degree of moisture of the air, is the ratio of the 

 quantity of vapor contained in the air to the quantity it could contain at the tem- 

 perature observed, if fully saturated. 

 If we call 



The force of vapor contained in the air =y", 



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 



/x^ioo _ Rgij^fiye Humidity in Hundredths. 



But as -^^, — =:fx -p , it is obvious that the operation indicated by the former 

 expression, viz, -^^ — , 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 to the tensions. 



The following Table, taken from the Annuaire Meleorologique de la France, for 

 1850, p. 79, gives the factor p for every tenth of a degree from — 10 to -(-35° 

 Centigrade, corresponding to the Forces of Vapor in Table I. 



Use of the Table. 



The force of vapor contained in the air being given in millimetres, multiply the 

 number expressing it by the factor in the table corresponding 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 = 24° Centigrade. 



" " force of vapor in the air to be =; 10.76 millimetres. 



Opposite 24° is found in the table the factor 4.51. 



Then 10.76 x 4.51 = 48.5, Relative Humidity in Hundredths. 



2. Suppose the temperature of the air to be = 16.7. 

 " " force of vapor in the air to be = 12.07. 



Table gives for 16.7 the factor 7.07. 



Then 12.07 x 7.07 = 85.3, Relative Humidity. 



B 36 



