104 VAPOR NUCLEI AND IONS. 



in the fog chamber by radium and decay in the lapse of time after the 

 radium is suddenly removed. The decay curves all show minima for a 

 drop of pressure above the fog limits of dust-free air; while the curve is 

 normal for pressure differences below the fog limit. 



If the coefficient of decay for the ions within the fog chamber is the 

 same as that found by purely electrical investigations, and if the relative 

 numbers of nuclei corresponding in a given apparatus and given con- 

 ditions of exhaustions are known, then a new method for the standard- 

 ization of coronas in terms of the number of nuclei involved in their 

 appearance, is suggested; for 



m = (n /n-i) bt 



if and n are two successive nucleations observed under like conditions 

 at t seconds apart and if b is the known coefficient of decay. Conversely, 

 if n is given this method lends itself for the determination of nucleation 

 ratios n /n, and for the experimental determination of the distribution 

 of a given mass of precipitated water on groups of nuclei different in 

 average size one of the important of the outstanding problems. 



Finally, it was shown that data bearing on the graded character of the 

 colloidal nuclei of dust-free air may be obtained most directly and 

 throughout the widest range from the behavior of the inclosed steam 

 jet. If {ccet. par.) the steam pressure is intensified until the originally 

 clear field (air dust being practically inactive), after passing a succession 

 of colors, becomes clear again in consequence of absence of all con- 

 densation, it follows that colloidal nuclei in vast numbers and of contin- 

 ually decreasing size must successively become available for condensation 

 until the fog particles are too small to be optically discernible. Each 

 particular color corresponds to a group of colloidal nuclei characterized 

 by their minimum size. It is still to be determined, however, whether 

 these nuclei belong to the system of saturated vapor, or to the air, or to 

 both. 



