CHAPTER I 



EARLY SUCCESSIVE STAGES OF THE EFFICIENCY OF THE FOG CHAMBER 



AND ALLIED RESULTS. 



Before beginning the main subject of this chapter (see section 2), it 

 is advisable to add a few measurements of the distributions of ions pro- 

 duced within the fog chamber by the X-rays or by radium acting from 

 without, since these occurrences must be kept in mind throughout the 

 measurements. Again, the effect of different classes of nuclei (persistent 

 nuclei, ions, and colloidal nuclei) in presence of each other is similarly 

 important and direct light must be thrown upon it preliminarily. 



Under all conditions the fog chamber is attached to a large vacuum 

 chamber by a rigid passage-way of the length and diameter specified, the 

 ratio of the volumes of the two chambers being about as 6 to 100, respec- 

 tively. Moreover, it was customary to read off the drop of pressure (dp) 

 at the fog chamber (isolated immediately after exhaustion from the 

 vacuum chamber) when isothermal conditions had been reestablished. 

 The observed datum suffices for the comparisons of nucleation when the 

 same chambers are used throughout; but it will be shown in Chapter II 

 that it is much in excess of the true drop of pressure and that the latter 

 is to be computed from the initial pressures in fog and vacuum chambers 

 and the final pressure when both are in contact, all under isothermal 

 conditions. 



After completing the work of section 2 of this chapter, a few appli- 

 cations were made with the apparatus in its state of partial completion 

 for the purpose of ascertaining whether there is any discernible change 

 of colloidal nucleation and by implication of ionization in the stagnant 

 air within the scope of the method. Several months of observation 

 showed none. The early data have been added to the chapter for 

 convenience in chronology, though the)' slightly interrupt the continuity 

 of the research. The question of time variation is taken up again by a 

 different method in Chapter VI. 



DISTRIBUTION OF NUCLEI WITHIN THE GLASS FOG CHAMBER, WHEN 

 THE AIR IS ENERGIZED BY THE GAMMA-RAYS OR THE X-RAYS. 



I. Introductory. I may recall at the outset that there are three 

 classes of nuclei to be considered in this chapter, the first of which 

 includes the ordinary dust-like or persistent kind. They may be sepa- 



