REFRACTIVITY TABLES 397 



Now interpolating for humidity, 



N{850, 22, 50) = 280.3 N units. 

 Since 



A^(850, 22, 50) - Z)(850, 22) = T^(22, 50), 



thus 



TF(22, 50) = 280.3 - 223.6 = 56.7 N units, and 

 TF(22, 47) = 56.7 (47/50) = 53.3 A^ units. 



Adding 



T^^(22, 47) to i)(980, 22) yields 



A^(980, 22, 47) = D(980, 22) + IF(22,47) 



= 257.8 + 53.3 = 311.1 N units. 



Substitution directly into (1.20) and use of the Smithsonian Meteor- 

 ological Tables [2] for vapor pressure yields the identical result to four 

 significant figures. 



A^(980, 22, 47) = 311.1 A^ units. 



Ambient recording thermometers generally read to a tenth of a degree 

 centigrade. Rounding the temperature to the nearest whole degree 

 introduces an extraneous error into the interpolation process. At 45 °C, 

 1000 mbar, and at a relative humidity of 100 percent, this error will have 

 a maximum of 7.7 A^ units. However, these conditions are an extreme 

 rarity climatologically speaking, and at normal temperature ranges an 

 error of more than 2 N units is unlikely. 



