6 Introduction. 



has also been helpful in the wording of headings and the section on 

 description and uses of the tables. 



Acknowledgment is made to Professor G. W. Pierce, of Harvard 

 College, for his advice in the preparation of the tables of physical 

 constants. 



DESCRIPTION AND USE OF TABLES. 

 TABLE 1. Conversion of seconds to decimal parts of a minute. 



This table is obtained by dividing the number of seconds by 60 and 

 expressing the result to the nearest 0.01 minute. It is useful where 

 time is observed in minutes and seconds and where it is necessary in 

 computation to convert to minutes and decimal parts. The same 

 table can be used to ascertain the decimal fraction of an hour corre- 

 sponding to minutes. 



TABLE 2. Pressure of aqueous vapor at dry-bulb temperatures 

 15 to 25 C. for relative humidities between 30 and 75 per cent. 



This table gives the pressure of aqueous vapor in millimeters of 

 mercury to 0.1 millimeter for temperatures of the dry-bulb ranging 

 from 15 to 25 C. and of the wet-bulb from 8.0 to 21.9 C. It is 

 mainly useful for obtaining from the readings of a wet-bulb and dry- 

 bulb psychrometer the partial pressure due to water-vapor when the 

 gas is neither saturated nor dry and it is desired to calculate the re- 

 duction of the volume to 760 millimeters dry. Its practical appli- 

 cation is in connection with experiments with respiration chambers. 

 The side argument is for the dry-thermometer readings to 0.1 C. and 

 the top argument gives the readings of the wet thermometer to 0.1. 



TABLE 3. Pressure of aqueous vapor at saturation. 



The table gives the pressure of water-vapor in 0.01 millimeter 

 mercury at temperatures to 0.1 C., ranging from 10.0 to 36.9 C., 

 when a gas is completely saturated. It is useful in calculating the 

 reduction of gas volumes to 760 millimeters dry when they are 

 observed under the conditions of complete saturation at any given 

 temperature. In combination with table 2, relative humidities can 

 be calculated (within 1 per cent) by dividing the millimeters pressure 

 at the given wet-bulb and dry-bulb thermometer readings by the 

 millimeters pressure for saturation at the temperature of the dry- 

 bulb thermometer. The result multiplied by 100 will give per- 

 centage relative humidity. The top argument gives the 0.1; the 

 side argument 1.0. The table is from Smithsonian Physical Tables, 

 1920, pp. 183, 184. 



