DISTANCE EFFECT. 



13 



was provided with a lid to be opened or closed at pleasure. When the 

 distance is D = $o, about 8 per cent of the radiation passes through; 

 when D = io cm. the amount is about 17 per cent. Unfortunately the 

 observation through the window is not satisfactory and no doubt a 

 certain amount of radiation enters here secondarily. It is therefore 

 difficult to carry out the comparison. 



Table 6. Penetration through lead. Lead-cased glass fog chamber. Plates of lead 



0.14 cm. thick. 5^=24.5. 



I,ead case 



On; end closed 



On; end open. 



On; end closed 



On; end closed 



On; end closed 



Off; plate only 



Off; no plate. . 



D. 



50 



50 

 10 

 10 

 10 



15 



15 



j. 



2-7 



3-i 



gB P. 



3-8 



3-5 



3-5 

 w o g 

 g BPto 

 w P cor. 



7.0 



Large coronas near brass cap. Secondary radiation. 



11. General inferences. The occurrence of a continuous succession 

 of groups or gradations of nuclei in the curve of figs. 6 and 7, each of 

 which groups constitutes a condition of chemical equilibrium for the 

 given radiating environment, is suggestive. In the first place, it may be 

 recalled that the nuclei of dust-free air are an essential part of this body 

 as much as the molecules themselves. Such nuclei, if withdrawn by 

 precipitation, are at once restored. Again, air left without interference 

 for days shows a maximum of this nucleation for the given conditions of 

 exhaustion when all foreign nucleation must have vanished. Indeed, 

 the water molecules themselves may be treated as a continuous part 

 of the nucleation in question, the frequency of occurrence being a maxi- 

 mum for the molecular dimensions. It is best, however, to reserve dis- 

 cussion for a later paragraph (section 43). 



THE NUCLEATION OF FILTERED AIR IN RELATION TO DIFFERENT 

 SUPERSATURATIONS OF WATER VAPOR. 



12. Successive series of results. Before proceeding with an account 

 of the change of the efficient colloidal nucleation of atmospheric air in 

 the lapse of time and other like problems, it is expedient to consider the 

 behavior of filtered air when subjected to different exhaustions. I will 



