DISTRIBUTION WITHIN FOG CHAMBER. 5 



per cent, respectively, the nucleation within is about constant through- 

 out the 45 cm. of length of cylinder. At least an internal drop to less than 

 one-fourth is out of the question, as the diagram shows. It must be 

 remembered that the nucleation is produced instantly to saturation, that 

 all nucleation will vanish with the removal of the radium to infinity 

 within a few seconds, and that the ions here in question are relatively 

 large nuclei as compared with the colloidal nuclei of dust-free air. The 

 latter, moreover, are quite ineffective at the observed pressure differ- 

 ence, dp = 21, used. If larger pressure differences appear the results are 

 usually quite different. 



3. Explanation. To account for these remarkable results is difficult. 

 Convection is probably out of the question, though it will be quite elim- 

 inated in the following experiments. One may hazard the suggestion 

 that the effective agency outside of the cylinder are the gamma-rays 

 directly, whereas within the cylinder the ionization produced by those 

 rays secondarily is in question. In other words, the gamma-rays do not 

 act here directly, but the nuclei are produced by corpuscles set free by 

 these rays. The medium within the cylinder is thus in a state resembling 

 an electrolytic medium having the same ionic pressure throughout. 

 It is this ionic pressure depending on the density and speed of the cor- 

 puscles which is transmitted instantaneously from end to end of the 

 cylinder. To refer to the phenomenon as diffusion would be obscure 

 without a statement as to what diffuses. The ionic nucleus is relatively 

 a fixture and could not diffuse, in the time specified, to the far end of 

 the cylinder, quite apart from decay. 



4. Further experiments with radium. High exhaustions. In the 



preceding experiments the wet cloth partition was about 10 cm. above 

 the surface of the water below. In the new chamber shown in fig. 3, the 

 distance has been reduced to 5 cm. Under these circumstances a very 

 marked gradation of the number of efficient nuclei was observed for the 

 first time. This is not, however, due to the supposed elimination of 

 convection, but rather to the large pressure difference applied in the 

 experiments. The result follows in table 2. When the radium tube is 

 placed at T (fig. 1) symmetrically on the side, the metal cap virtually 

 becomes the source of nuclei, or better, it seems to become secondarily 

 active more intensely than the remainder of the glass chamber. The 

 coronas obtained with two goniometers at distances 1 1 and 36 cm. from 

 the brass end and 35 and 10 cm. from the glass end are rapidly larger as 

 the brass end is approached. The ratios of the n- values is greater than 

 2:5. These conditions are retained indefinitely so long as the radium is 



