474 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. SI 



of constant quantity of saturation for the varying values of p and 

 t. The associated values of p and t for the individual curves of 

 saturation, which latter we can for brevity call "gram-lines" or 

 lines of equal quantity of moisture, are obtained for individual 

 gram-lines from table I, page 486. Fig. 3 is constructed by the 

 values of table J. 



Table J 



The curves of gram-lines are feebly curved and run nearly parallel 

 to each other. The distances between them for equal differences 

 of w r eight increase approximately logarithmically corresponding to 

 the curve e m = f (t). 



700 

 -30° -20° -J0° 0° JO" 20° 30° 6 ° 



FIG. 3. GRAM-LINES OF SATURATION 



These saturation curves may also be transferred to another net- 

 work of coordinates whose vertical axis, as before, shows the pres- 

 sure while on the horizontal axis the number of grams is shown. 

 In this case therefore p and x are the variable coordinates in the 

 equation 



e - f (t) = 



xp 

 622 -f- x 



constant, 



