8 CONDENSATION OF VAPOR AS INDUCED BY NUCLEI AND IONS. 



The data for p lt etc., are given in table 3, and are shown in the graphs 

 of fig. 2, whence their differences from fig. i may be ascertained. The 

 respective pressures holding for p f 45 cm. are also shown in a notched 

 curve and will be further elucidated. The ratio dp 2 /dp 3 of the isothermal 

 and adiabatic drop is here (table 3) about 0.68, or of the same order as 

 in table 2. 



TABLE 3. Definite computations corresponding to table 2. ^ = 76 cm.; 2=20; 

 ?r=i-7; r/T l = (p/p l ) l -c'k, and T/T'i = (p/p'i) l ~ c/k assumed. 



6. Approximate computation of r^ To find the temperature of 

 the fog chamber after the adiabatic temperature r t has been raised by 

 condensation of fog to T I} it is apparently necessary to compute p 2 

 first, and then proceed by the method used by Wilson* and Thomson. 

 When the vacuum chamber is large, however, its pressures vary but 

 slightly, and therefore the pressure observed at the vacuum chamber 

 after exhaustion, p 3 , when the two chambers are in communication, is 

 very nearly the adiabatic pressure of the fog chamber, p v This result 

 makes it easier to compute not only r lt but incidentally the water, m, 

 precipitated per cubic centimeter (without stopping to compute the 

 other pressures), with a degree of accuracy more than sufficient when 

 the other measurements depend on the size of coronas. 



To show this, let d, L, and 71 refer to the density, latent heat of 

 vaporization, and pressure of water (or other) vapor; let p, k, c, r, 

 denote density, specific heat at constant pressure, specific heat at con- 

 stant volume, and absolute temperature of the air, the water vapor 

 contained being disregarded apart from the occurrence of condensation. 

 As above let the variables, if primed, belong to the vacuum chamber, 

 otherwise to the fog chamber. Let the subscripts, etc., also be similarly 

 interpreted, so that d is the known density of saturated water vapor at 

 T absolute. 



*C. T. R. Wilson: Phil. Trans., London, vol. 189, p. 298, 1897. 



