EFFICIENCY OF FOG CHAMBER. 25 



Accordingly the inch stopcock was replaced by a i^-inch plug gas 

 cock, retaining the same inch tubing. The resistance in this case 

 was least at the stopcock, which accounts for the remarkable steadi- 

 ness of the results obtained in successive exhaustions. 



Furthermore, the fog chamber was modified by inserting three wet 

 cloth partitions, horizontal and about 5 cm. apart, as shown in fig. 3. 

 The new form was not merely favorable to better saturation, but all con- 

 vection currents were more effectually cut off. This was at first (though 

 incorrectly) supposed to be the reason for the appearance of distribu- 

 tions of nuclei within the chamber produced by the action of radium kept 

 outside of it, a result already detailed above, but which here appeared 

 for the first time in a very marked degree. In the later experiments 

 four cloth partitions were inserted, as in fig. 4. 



The results are given in the successive parts, table 10, in the usual 

 way, dust-free air being examined with and without the interference 

 of external radiation. It is not probable that any errors are now intro- 

 duced by the filter. 



In view of the intense ionization used, the usual cycle of measurable 

 coronas is exceeded, and the resulting data become more and more 

 fully relative, both on this account and because of the high pressure 

 differences applied. Absolute values are, however, of little interest, and 

 it is precisely from the relations obtained that conclusions are to be 

 drawn. The quantities s, n, N, dp have been frequently defined. D 

 is measured from the side of the apparatus, so that all action takes place 

 through 0.3 cm. of glass. No aluminum screen was interposed. 



18. Remarks on the s=curves. Non=energized air. The present 

 5-curves for non-energized air, fig. 19, are in strong contrast with the 

 preceding. Variability in the lapse of time has been nearly eliminated. 

 The curves have moved bodily somewhat farther to the left into the 

 region of smaller supersaturations, as is shown by comparison with the 

 dotted line in fig. 19 (taken from the preceding fig. 15), evidencing the 

 increase of efficiency referred to. The curves of fig. 19 are in remarkable 

 contrast with the preceding in two respects; they reach a definite 

 asymptote at about dp = 35, which is retained until the pressure difference 

 is so high that other complications step in. There is certainly an incre- 

 ment after dp = 30, as proved by the change of coronas. Whether this 

 limit is due to a cessation of further drop of temperature in the appara- 

 tus, or whether a distinct group of colloidal air nuclei is in question, 

 remains to be seen. The possibility of the continued succession of 

 groups of this kind is not, a priori, improbable. 



