6 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



differences the sizes of captured nuclei are smaller, until the air mole- 

 cule itself is approached. It follows, then, that normal dust-free air 

 always contains unstable systems. 



Hence the question may well be asked whether very sudden and 

 intense exhaustion may not itself possibly be productive of nuclei. 

 Thus, if an unstable molecular configuration is just about to break 

 down, it is conceivable that the tendency to break down is accentu- 

 ated by the violent treatment in question. 



We made some experiments on this subject, by looking for the 

 presence of ionization under these conditions, using a pressure differ- 

 ence, Sy!>>3o cm., by placing a gold-leaf electrometer, properly insu- 

 lated, in the condensation chamber. The loss of charge in damp air 

 is at first surprisingly small ; nevertheless the experiments are very 

 difficult and we were unable to come to a conclusion. 



8. Successively increasing: times of exposure to X-radiation. After 



this digression, experiments were resumed with the apparatus, as 

 shown in figure i. The pressure difference, S/>=i7 cm., was used 

 throughout, as this is well within the lower limit of spontaneous con- 

 densation for the given receiver, while coronas may be obtained with 

 X-ray nuclei for pressure differences even lower than 8p=io cm. 

 Such coronas are vague, however, until the rain nuclei are thrown 

 out, and on second exhaustion (n = 39,000, 5 = 4.8 were usual values 

 after 4 minutes of exposure to the radiation) they are naturally faint. 

 The immediate incentive to the work of the present section was 

 given by the occurrence of elliptic distortions of coronas, as shown 

 in the following tables : 



TABLE 6. Distorted coronas, Increasing times of exposure to X-rays. Sp = 17 cm. 

 Coronal center 19 cm. (A side) and 46 cm. (B side) from bulb. Angular aperture 

 = 5/30. 



Time, 2 min. 



Side, A B 



First exhaustion, .5 = 4.5, elliptic, strong. i.o? faint, circular. 



Second exhaustion, 5 = 2.7, circular. 2.4 circular. 



First exhaustion, .5 = 4.6, elliptic, strong. o.o 



First exhaustion, 5 = 4.6, elliptic, strong. o.o 



TABLE 7. Preceding table continued. 

 Time, i min. 2 min. 3 min. 



Side, ABA B A B 



5= 3.1, round, o 4.1, elliptic, o 5.8, ellipse, larger o 



strong. strong. and distorted. 



On second exhaustion, after refilling with filtered air, the coronas 

 were nearly identical on both sides. 



