EVAPORATION OF ATOMS 



369 



in terms of the vertical displacement 5 of a point P from the line OA or the 

 displacement 8' from the horizontal line BC. If we let /i be the abscissa 



t (tiiDQ) 



Fig. 26. Curve and construction describing Eqs. (43) to (45) used in 

 calculation of transient curves. 



corresponding to the intersection M of OA and BC, our equations become 



exp (J/5) = 1+exp IIix{tx-t)/(jAi (44) 



and 



exp (//5') = l+exp//M(^-/i)/'^Ai. 



(45) 



Thus at points P and P\ which are displaced from MN by equal horizontal 

 distances, but in opposite directions, 8 and W are equal. The slope of the 

 tangent to the curve at N is one-half the slope of the line OA. 



The full line curves which branch off from the lines I, II and III in 

 Fig. 24 have been accurately calculated by these equations without the use 

 of adjustable parameters. 



The nearly perfect agreement of the points with the curves proves that 

 the transient states during the condensation and evaporation of caesium 

 atoms from these concentrated films are determined by the balance between 

 the rates of condensation and evaporation as given by Eq. (38). 



These experiments also prove that the surface phase postulate (S.P.P.) 

 is applicable to these films. The agreement between the calculated curves 

 and the experimental points shows that v^ is determined by 6 and T in 

 accordance with Eqs. (6 to 10) and does not depend on the manner in 

 which Q has been reached; i.e., by condensation or by evaporation. 



