10 CONDENSATION OF VAPOR AS INDUCED BY NUCLEI AND IONS. 



and the small quantity involving the vapor pressures TT treated as a 

 correction. It amounts to about i per cent of the large quantity. The 

 values of p 2 are also given in the table and chart. This shows that p 2 

 observed is always smaller than p 2 computed, even when allowance 

 is made for the condensation of water; i. e., the fog chamber begins to 

 appreciably heat itself above the temperature T X before the cock can be 

 closed again, so that when isolated it contains less than its proper 

 quantity of air. Only the initial and the final (both chambers com- 

 municating) pressures may therefore be taken at the fog chamber. 

 (Cf. section 9.) 



\ 



8. Rate of reheating of fog chamber. There is a final question 

 at issue, relating to the rate at which heat flows into the adiabatically 

 cooled fog chamber. Experiments may be made by opening the exhaust 

 cock for stated lengths of time t. The vacuum pressure being p' = 48 . 6, 

 the datum for t = o second may be computed as 2 = 57.8 cm., or after 

 condensation 2 = 52.4 cm. Table 4 contains the results, and they are 

 fully mapped out in chart, fig. 3. The notched curves show the suc- 

 cessions of pressure in both chambers. Neither p 2 nor p' 2 may be ob- 

 served, since the chambers communicate during the opening of the stop- 

 cock for a period certainly longer than o . i second. Observable pressures 

 are shown on the vertical line below p 2 and above p' 2 . Hence within 

 a quarter of a second the final isothermal pressure (/ = oo , chambers 

 communicating) is already regained to more than 60 per cent, and this in 

 spite of the fact that the capacity of the fog chamber is over 6 liters. 

 Hence the attempt to observe p 2 (isothermal temperature after con- 

 densation) at the fog chamber is idle. It practically reaches p 3 if the 

 exhaust cock is open about 10 seconds. The pressure p 2 is never reached, 

 yet p 2 is exceeded, owing to the counteraction of the vacuum chamber. 

 Finally p l may be virtually read off in case of a large vacuum chamber 

 by adding a slight correction for p 3 . This is one of the advantages of the 

 method. 



TABLE 4. Rate of heat influx. Barometer, 76.0 cm. 



From chart ' = 48.6; /> 2 = 57-8; /> 2 = 

 'From the chart />' 1 = 5O.2; p' 3 =$o.o. 



cm. 



