52 



A CONTINUOUS RECORD OF ATMOSPHERIC NUCLEATION. 



If the exhatistion at the time, t, is made from air pressure, po to p', cor- 

 responding to the temperatures 5„ and S', the relation is approximately S'Z-^o 

 = (/''/?°)'* '^ *" where a correction for precipitated liquid, etc., is needed. 



The vapor pressure corresponding to the reduced temperature, S', so ob- 

 tained after division by the saturation pressure at S^, is, then, the value of p 

 in equation (i), which therefore, like x and t, is known, so that k may be 

 computed. 



3. Application ami data. — In order to have an example for use in the 

 discussion below, I com-jnited the case for water vapor, which though unsuitable 

 from its lightness for experiment, is convenient for comparison with other 

 vapors, almost all of which are heavier than air. The well-known expansion of ( 1 ) , 



i'=i-nr'V2(fe0'"--^-V3X8(fe0^'=+^V3X5X32(fe0'^^ :■ 



judiciously manipulated is sufficient for the pur]:)ose, though I afterwards 

 availed myself of the tables in Dienger's Method of Least Squares in the absence 

 of larger tables. 



The results for water vapor were given in a table, with the time, t, in tnin- 

 utes and the height of the fog-bank, x, in centimeters. 



The table also contained a second series of data, for the case in which the 

 diffusion takes place into a vapor | saturated, to which reference will be made 

 below. The results of the table may be constructed graphically, showing re- 

 spectively the advance of diffusion at a given height and at a given time. The 



m 



T7\ 



a g 



1 



A 



-L 



.: I -C 8 -Z } 6 & Ui 



Figure i. — Diffusion- Chamber. 



Figure 2. — Ch.\rt Showing the Vapor Pressures, p, at Different Heights, x, in the Lapse of 

 Time, when Water Vapor Diffuses into Air. 



Figure 3. — The Same, for Diffusion into Air Originally i Saturated. 



latter are exhibited in figure 2, in connection with figure i. From either set of 

 curves the parabolas which show the rise of a given vapor pressure in the lapse 

 of time may be obtained by graphic interpolation. 



