6o 



VAPOR NUCLEI AND IONS. 



= 0.7745 



= 0.7782 



Mean 

 0.225 



In view of the low temperature (t x ) the vapor pressure (7^) may be 

 neglected for the fog chamber; but this would not be the case of the 

 vacuum chamber, where 7t\ is quite appreciable. As the result of this, 

 the march of pressures in the vacuum chamber is peculiar, but need 

 not be considered here, where p, p' ', p 3 , and p 2 are chiefly in question. 

 The difference between dp = p- p 3 as observed and dp c = p - p 2 as 

 computed now actually vanishes with the former (see fig. 29). In 

 other words, very nearly 



*-** = 0.77s, or *"* 



P-.Pi 



P -Pi 



0.225 



and therefore dp -dp c =0.225 op , nearly. Hence this is a correction 

 to be taken by preference. A table giving 0.225 dp for the usual ranges 

 of observation was therefore drawn up and used throughout the follow- 

 ing work, or the factor 0.775 may be used at once. These corrections 

 are quite sufficient to indicate that the efficiency of the fog chamber as 

 used above is not surpassed by any apparatus. 



The preceding correction, in comparison with the cases of sections 46 

 and 47, seemed to me to be most nearly in keeping with the actual state 

 of the case. The more nearly rigorous solution, when the air in both 

 chambers is continually saturated, leads to transcendental equations for 

 the adiabatic pressures (pi = p'i), which can only be obtained approxi- 

 mately. If the vapor pressures (7^ and tc\) correspond to p x and p\, 

 the results would be 



(*i - *>,)'/* - 



(pn-x)(i+v/V) 



(p'-7:)( k - c )/ k +viv.(i-(.K l ^\)/(p l -7[\)y/Hp-^ k - c y k 



(*>i-*i) e /*- 



(p 9 -n) (i+v/V) 



(i-(7r / 1 -^ 1 )/(p 1 -7r 1 )) c /*(p , -7r)(*- c )/&- r -u/y.(/>-7r)(*- c )A 



where approximate values must be entered for 7:\, 7r 1( p lt in the denom- 

 inator on the right side of the equation. 



