90 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



where the decrease is about inversely as the distance, except at long 

 distances, when the data become uncertain. All this is in strong 

 contrast with the X-ray effect, where the removal of the bulb to a 

 distance is so much less significant than the presence of a dense screen 

 in the path of the rays. 



72. Distribution of nucleation along the axis within the fog chamber. 



This makes a final anomalous feature of the results. Whereas the 

 nucleating effect falls off nearly 25 per cent when the radium is placed 

 axially at a distance of 40 cm. from the end of the fog chamber, out- 

 side of it the size of the coronas is about the same from end to end of 

 the inner length of about 40 cm., no matter what may be the position 

 of the radium outside.* It will be remembered that the decay and gen- 

 eration of the nucleus is so nearly instantaneous, that convection or 

 like discrepancy is quite out of the question. These observations are 

 difficult because of the short length of the chamber and the rapid sub- 

 sidence ; but so far as they have gone, there seems to be an entire 

 contrast between the behavior of the radiation outside of the chamber 

 and the behavior inside of it, the aluminum tube being in every case 

 outside of the chamber and axial in position. 



SUMMARY AND CONCLUSIONS. 



73. General remarks. The results of this chapter relate to fleeting 

 nuclei (ions), to persistent nuclei, to fog limits, to persistence of fleet- 

 ing nuclei or ions on solution, to the alternations of large and small 

 numbers of efficient nuclei in successive identical exhaustions, to the 

 secondary generation of nuclei after intense X-radiation, to the dis- 

 tribution of radiation in the space surrounding the X-ray tube in con- 

 trast with the corresponding case of the sealed tube with weak radium, 

 to the nucleation produced by the gamma rays and its distribution 

 within the fog chamber, etc. They are thus of considerable impor- 

 tance in their bearing on the present research, and will therefore be 

 advantageously summarized at the end of this memoir, in Chapter VI, 

 section 91 et seg., in connection with other relevant matter. 



* The statement in the text needs correction. My recent experiments have shown 

 that there is an axial gradation of the number of fleeting nuclei within the fog cham- 

 ber. This gradation becomes very marked when the fog chamber consists of parts 

 which are unequally strong secondary radiators. Discussion will be made elsewhere. 



