C. Bar-us — Large and Small Coronas. 351 



borne out : while the s-curves usually tend to reach an asymp- 

 tote or a maximum, the N-curves (number of nuclei per cm 3 com- 

 puted for normal pressure and temperature) do not usually do 

 so, at least so far as observed in the case of non-energized air. 



5. Blurred coronas. — The occurrence of an abundance of 

 rain with all the coronas, as well as the blurred appearance of 

 the coronas themselves, shows that gradation of particles is a 

 characteristic feature with all these condensations. The follow- 

 ing results for periodicity apparently indicate the presence of a 

 group of markedly large particles in the amount of about 1/8 

 or more of the total number of nuclei. 



6. Time loss of nuclei. — In the lapse of time exceeding even 

 half an hour (cf. fig. 5) the aperture of all coronas usually 

 diminishes in marked degree. Above the fog-limit, however, 

 the coronas do not vanish as the result of repeated exhaustion ; 

 i. e., the air can not be freed from nuclei by being stored in a 

 closed vessel. What is particularly remarkable is the rapidity 

 with which « nuclei precipitated by condensation are again 

 replaced. Whether these come through the filter in quasi- 

 gaseous form, or whether they are spontaneously produced in 

 the imprisoned air is yet to be decided. In every case some- 

 thing has to be explained away. If the nuclei came through 

 the filter, for instance, they would not come periodically. If 

 inferior coronas were due to undersaturation, superior coronas 

 should be obtained in the lapse of time ; the reverse of which 

 is observed. 



7. Effect of pressure difference. — With increasing pressure 

 differences, op, the superior and the inferior apertures each lie 

 on distinct curves, as in figures 6 and 7, both of which rise 

 rapidly at first, are then rapidly retarded and tend to reach dis- 

 tinct maxima. The limiting ratio of apertures is liable to be 

 nearly one-half. If, however, the pressure difference is carried 

 far enough, both ^-curves sometimes change character by 

 decreasing and increasing respectively, eventually to reach a 

 common value. If then pressure difference is in turn reduced 

 from these final values, the oscillation of s is usually absent and 

 a mean nucleation appears at all subsequent (decreasing) pres- 

 sure differences. 



8. Continued. — The increase of nucleation, n, or N, with 

 the pressure difference, 8j), is often difficult to interpret, since 

 the inferior and superior values are so much more widely and 

 irregularly distributed. The ^-curves usually show two limit- 

 ing rates of increase of n with hp, respectively very large and 

 very small. This is particularly well brought out in the data 

 of figure 7 where both loci are nearly straight even above 

 Bp = 40 cm . Inferior coronas are sometimes absent and those 

 observed present an accentuated case of superior corona ; and 

 vice versa. 



