VAPOR NUCLEI AND IONS. 



(Welsbach mantle) was 250 cm. beyond the fog chamber. Usually the 

 angular diameter of the coronas is about 5/30. In table i, 5 t refers to 

 the goniometer nearer the radium, s 2 to the other, and N t and N 2 are the 

 corresponding nucleations, when D is the distance of the radium tube 

 from the end of the cylinder. 



After the influx of filtered air, time was always allowed for the dissi- 

 pation of convection currents. There was some difficulty in reading both 

 goniometers consecutively without loss of time, as the small coronas soon 

 vanish with the subsidence of the fog particles. It was necessary to 

 cleanse the walls carefully before beginning the work to obviate deposits 

 of dew. 



D 



R 



Fig. i. 



-30 



-20 -10 



Fig. 2. 



20 



30 







"ft' 



i4- 



fr 



p 



)e *h - 



Jt 



# 



Fig. 3. 



Fig. 4- 



Figs, i, 3, 4. Types of cylindrical fog chamber. Axial section. E, exhaust pipe; 



c, cloth partitions. 

 Fig. 2. Nucleation (A/) due to weak radium at different distances from and on top 



(side of cylinder) of the fog chamber. Table 1. 



The table gives evidence of a small difference between N l and iV 2 , but 

 this is here unquestionably an observational error, particularly as its 

 sign is often reversed. The chart (fig. 2) then shows the mean number 

 of nuclei within, when the radium is at D = o, 20, and 40 cm. from the 

 end; and while the nucleation drops off rapidly from 100 to 45 and 24 



