PSYCHROMETRICAL TABLE. 141 



2. By observation we have, 



Dry Thermometer = 50° F. 



Wet Thermometer = 40° F. 



Difference == 10° F. 



Then, by Glaisher's table, we find. 



Force of Vapor = 0.186 inch. 



Relative Humidity ^ 0.495 

 And by Guyot's table, we find, 



Force of Vapor = 0.117 inch. 



Relative Humidity = 0.322 



3. The reading of the 



Dry Thermometer is = 90° F. 



Wet Thermometer is =z 70° F. 



Difference = 20° F. 



By Glaisher's table we have. 



Force of Vapor = 0.523 inch. 



Relative Humidity = 0.381 

 And by Guyot's table, 



Force of Vapor = 0.464 inch. 



Relative Humidity == 0.329 



The temperatures of the Dew-Point, given in Glaisher's tables, have been com- 

 puted by means of the empirical factors given below, page 140, and in the manner 

 there described. See Preface to the Table, page 11. 



Arrangement of the Table. 



In the first two columns, at the left, are found the indications, in degrees of Fah- 

 renheit, of the dry and wet bulb thermometers. In the following columns, in their 

 order, and opposite to each of the temperatures of the wet thermometer, are given 

 the temperature of the dew-point ; the force of vapor, in English inches ; the weight 

 of vapor, in grains, contained in a cubic foot of air ; the amount of the same required 

 for saturation ; and the relative humidity in thousandths, corresponding to the differ- 

 ence of temperature between the two thermometers. The second half of the page, 

 at the right, furnishes, in seven columns, the weight, in grains, of a cubic foot of air, 

 under various barometric pressures from 28 to 31 inches, and in the different hygro- 

 metric conditions indicated by the differences of the two thermometers. These 

 numbers have been computed in the manner described below, page 142. 



The range of the table extends from 10° to 90° of the dry thermometer, or of 

 the temperature of the air. From 10° to 34° Fahrenheit the results are calculated 

 for every second, third, and fifth of a degree of the wet thermometer, and for ex- 

 treme differences of the temperature of evaporation ranging from 2° to 5° below the 

 temperature of the air. From 34° to 90° the results are given only for every full 

 de^' ce of the wet thermometer, and for extreme differences gradually increasing 



a 105 



