128 CONDENSATION OF VAPOR AS INDUCED BY NUCLEI AND IONS. 



lower radiation (radiation at some distance, 40 cm., from the fog cham- 

 ber). Thus in fig. 42 curve c introduces low exhaustion dp 3 /p, curve b 

 low radiation, all of them the time effect. 



In fig. 43 the results of tables 50 and 51 have in fact been summarized, 

 the table giving b = (dn / dt') / n 2 and the nucleation n from which the 

 decay takes place. One may note the rapidly increasing values of b 

 when n is smaller and their tendency towards constant values when n is 

 larger, remembering always that the ionization is throughout low. 



75. Further experiments. Table 52, containing exhaustions above 

 the fog limit of air, fails to show the usual high values of b, for the ionized 

 nucleation eventually emerges into the vapor nucleation of dust-free air. 

 In table 53, however, the exhaustion is low enough to catch but few 

 vapor nuclei, while being high enough to insure large coronas due to 

 ions. The data are shown in fig. 44. Series II for low initial nucleations 

 is somewhat irregular, for reasons, as I afterwards learned, connected 

 with the precise position of the radium tube on the top of the fog cham- 

 ber. Series III for higher nucleations is smoother. Both, however, 

 confirm the occurrence of large values of b associated with small values 

 of n, no matter how the latter are obtained. 



If the true equation of the decay curve, dn/dt, were known, it would 

 be worth while to reduce all these data to a common scale. But fig. 43 

 shows that the values of b rather suddenly increase below io 3 w = io, so 

 that a simple relation is not suggested for the reduction. 



The question arises incidentally whether the ions may not vanish by 

 accretion, i. e., their number may be reduced because individual ions 

 cohere. In such a case the fog limits should be reduced, which is con- 

 trary to the evidence. There seems to be a second cause for decay 

 entering efficiently when the nucleation becomes smaller. We may 

 therefore pertinently inquire whether for large nucleation the decay of 

 ions in the fog chamber approaches the electrical value. 



76. Case of absorption and decay of ions. The most promising 

 method of accounting for the above results has been suggested by the 

 work in connection with the behavior of phosphorus nuclei.* There may 

 be either generation or destruction of ions proportional to the number 

 n present per cubic centimeter, in addition to the mutual destruction on 

 combination of opposite charges. In other words, the equation now 

 applicable now is 



dn/dt = a + en + bri* 



where a is the number generated per second by the radiation, en the 

 number independently absorbed per second, and bn 2 the number decay- 



*Barus, Experiments with Ionized Air, Smiths. Contrib. No. 1309, 1901, pp. 34-36. 



