4 6 



VAPOR NUCLEI AND IONS. 



The earliest results (Chapter I, section 12) scarcely captured the maximum 

 of 30,000 nuclei under the extreme exhaustion corresponding to the 

 limiting asymptote (marked "preliminary" in fig. 24). In proportion 

 as the apparatus was perfected, this asymptote was raised, step by step, 

 until nucleations of at least 500,000 were left in the exhausted fog chamber. 

 Probably the asymptote, or more accurately the terminal corona, obtained 

 in any given type of apparatus, indicates that the limit of condensing 



30 c 35 



DECR. SIZE+- 



Fig- 2 5 Smooth'curve from fig. 24. Nucleation (N) of dust-free air, in thousands of 

 nuclei per cubic centimeter, energized or not , as stated, by weak radium, or by the X-rays, 

 at different distances {D in cm.). The letters attached to the curves indicate the 

 characteristic colors of the inner field (or its margin) of the largest coronas, the order 

 of colors being R, O, Y, G, B. The abscissas show the observed isothermal drop of 

 pressure by which the supersaturation is produced and the nucleations applied rela- 

 tively to the given apparatus. The line marked "air" shows the behavior of dust-free 

 non-energized air terminating in the large green coronas. In a perfect apparatus 

 supersaturation would increase enormously beyond o; the droplets would be at freez- 

 ing beyond b. In the given apparatus efficiency probably ceases beyond c when damp 

 air is the medium. 



power has been reached. Between the fog limit and the terminal corona 

 the graph rises in a straight upward sweep; and it is remarkable that 

 the rates at which the nucleation decrease with the drop of pressure, or 

 better with the volume expansion, are about the same between fog limit 

 and asymptote, no matter whether they lie within the region of high 

 supersaturation characteristic of the colloidal nuclei or in the region 

 of relatively low supersaturation characteristic of ionized air. Moreover, 



