2 CONDENSATION OF VAPOR AS INDUCED BY NUCLEI AND IONS. 



lively. For this purpose fog particles precipitated on phosphorus nuclei 

 were successively evaporated as rapidly as possible by compression 

 (influx of air), so as to make the loss by subsidence negligible except at 

 the end of the series, when so few nuclei are present that the precipitate 

 is rain-like. In such a case the only loss of nuclei is due to the exhaustion, 

 as the normal time loss* is relatively small. In table i, taken from an 

 earlier report, f I have given a typical case, the exhaustion ratio being 

 y = o."jS, nearly. As dust-free air is introduced after each exhaustion the 

 successive nucleations are clearly in geometric progression. As long as 

 the nucleation is less than 100,000, subsidence may be disregarded, as the 



'0 4- 6 8 10 / 14- 1Q IS 20 



FIG. i. Chart showing the survival ratio, n'/n, in successive exhaustions, for 

 phosphorus nuclei (A, 2, 3,) and water nuclei (4, 5, 6, 7). Scale of latter magni- 

 fied ten times. 



curves A in fig. i show. The table also contains the angular diameters 

 (f> = 5 / 30 of the coronas and the nucleations n computed therefrom . Finally 

 the ratios n'/n of the successive nucleations n and n' are given in each 

 case. These should be equal to the exhaustion ratio if no other loss of 

 nuclei occurs. In fact, if we take the data above w= 100,000 the mean 

 ratio of the ten cases is n f /n = o.j6, agreeing practically with y = o.jS. 



If we plot the successive ratios n'/n in terms of n, the results show a 

 jagged curve oscillating about n' /n = o.'j&, but descending rapidly below 

 n = io 5 as the result of subsidence. (Compare curve A , fig. i .) The irreg- 

 ularity of the curve is inevitable, as it corresponds to a ratio between two 

 large coronas whose outlines are no longer sharp ; but there is compen- 

 sation in the successive values, as the curve, taken as a whole, indicates. 



*Compare chapter n. 



jCarnegie Institution of Washington Publication No. 96, chap, in, table 17, 1908. 



