STANDARDIZATION AND EFFICIENCY OF THE FOG CHAMBER. 



The endeavor to clean the fog chamber by successive exhaustion and 

 apparently complete subsidence failed utterly. Fog particles evaporate 

 before subsidence to persistent water nuclei, so that for small particles 

 (above the middle green corona), subsidence is negligible as compared 

 with evaporation, even in a long brass channel lined with a square tube 

 of wet cloth 4 cm. high and 4 cm. wide. 



20. Short tubes. Believing that any irregularity in the size of the 

 fog particles might be particularly harmful in the case of tubes 2 meters 

 long, short tubes of the same diameter were next tried in the endeavor 

 to obtain axial color effects with vapor nuclei. The results are given in 

 table 8. 



TABLE 8. Observations for axial color. Dust-free air. Vapor nuclei. Short brass 

 tube, 5 cm. diameter, 75 cm. long. Tube not cloth-lined. Part 15. Barometer 77.00 

 at 21. 



*The difference of fog limit or rain limit for descending and ascending Sp i s noteworthy. 

 tNo colors seen. Subsidence with a horizontal plane on top. 



The attempt again failed. No colors were observed, merely an evenly 

 subsiding, gradually (increasing dp] more intensely black fog. 



These results are disappointing. To obtain axial colors (coronas are 

 not observable longitudinally in tubes) ; it therefore seems essential that 

 drums of considerable equatorial diameter be used. In other words, the 

 vessel must not only be long but voluminous to obviate the radiation 

 effect from the walls after exhaustion, as much as possible. In fact, the 

 external layers of foggy air seem effectually to screen the interior from 

 the radiation. 



Incidentally a number of fog limits and rain limits were obtained, 

 which, however, present nothing new, except that on diminishing pressure 

 differences dp, the rain limit falls at a lower dp than on ascending differ- 

 ences. The appearance is as if the fine droplets generated nuclei. But 

 more probably very fine nuclei escape capture in the presence of coarse. 



Summarizing the above results, we may therefore conclude that the fog 

 particles producing the axial colors of coronas are of such a size as to 

 recall the interference phenomena of the lamellar grating, with which 

 their constants agree. 



The disk colors of coronas can not be similarly explained. 



The observation of axial color fails unless long, capacious fog chambers 

 are used. Tubes show opaque fields only. 



