i6 



CONDENSATION OF VAPOR AS INDUCED BY NUCLEI AND IONS. 



I purpose, therefore, in the present paper, to study the same phenom- 

 enon for an artificial barometer; in other words, to accentuate the 

 present discrepancies, let the pressure drop from a given upper limit to 

 varying lower limits, as well as from varying upper limits to a given 

 lower limit. The results so obtained are enormously different for the 

 same drop of pressure. Much of this would be anticipated; but the 

 question nevertheless arises whether the colloidal nucleation of the gas 

 is actually dependent in so marked a degree on its initial pressure, or 

 whether this dependence can be explained away. 



74 



76 



78 



10 



FIG. 4. Apparent nucleation of dust-free air in lapse of time. Apparatus I with 

 4-inch exhaust pipes; apparatus II with 2-inch exhaust pipes; otherwise identical. 

 A new and more pervious filter was installed on July n. The upper curve shows 

 corresponding barometric pressure within the fog chamber. 



Later in the course of the work I made additional comparisons with 

 the contemporaneous ionization of the air determined by Miss L. B. 

 Joslin and with the temperature of the fog chamber as distinguished 

 from the temperature of the air. These results as a whole finally showed 

 that a direct dependence of the vapor nucleation of the dust-free air 



