i8 



VAPOR NUCLEI AND IONS. 



13. Effect of X=rays and gamma=rays. Data. To interpret the above 

 results it will be necessary to vary the nucleations of the dust-free air 

 artificially, by acting on it from the outside of the chamber with the 

 X-rays, or with the gamma-rays of radium. 



In these experiments the glass fog chamber (fig. i), rigorously free 

 from leakage, was used with a framework of wet cloth within. Filtration 

 was throughout excessively slow and all other precautions were taken. 

 The radium in the hermetically sealed aluminum tube was pasted to the 

 top of the fog chamber at T. The X-ray bulb was adjustable, so as to 

 act from different positions at distances D. 



Table 8 shows results where dp is the pressure difference, 5/30 the 

 angular coronal diameter, when the distances of the eye and the lamp 

 are 35 cm. and 300 cm. from the fog chamber. The small distances D 

 (35 cm.) enabled the observer to see even the smallest coronas distinctly. 

 The nucleation n is obtained by supposing that the nuclei are restored 

 faster than they can be removed by exhaustion. In case of N this is not 

 the case, so that the correction for volume expansion is added. For 

 high pressure differences the absolute numbers are not trustworthy, but 

 the data given nevertheless show the relations satisfactorily. 



Table 8. Persistent nuclei. Exposure 2 m . D measured from anticathode to top 

 of fog chamber. Thick (1 mm.) aluminum screen (earthed) interposed. 



1 Spontaneous generation. 



2 Just visible before falling. 



The data of table 8 are constructed in the charts, figs. 15 to 17, showing 

 the s, n, and N curves in succession, for increasing supersaturations. 

 They will be useful for comparison with the advanced work below. 



14. Persistent nuclei. Table 8 gives the corresponding data for 

 persistent nuclei. Distances are here measured from the sides of the 

 fog chamber where the glass was thinner (about 0.2 cm.) than at the 

 end (1 cm.). No persistent nuclei were obtained when the radiation 



