86 



VAPOR NUCLEI AND IONS. 



ZOO 



180 



160 



400 



300 



100 200 300 400 500 600 



ZOO 



300 



400 



500 



Figs. 41, 42, and 43. Nucleations (ions) produced by a radiating X-ray bulb at 

 different distances (D) from the small wood fog chamber. Table 34. 



With regard to the work of table 34 it should be stated that it is 

 always customary to make a second exhaustion to remove the water 

 nuclei left by the first. Again but two distances (1 and 6 meters) were 

 selected to guard against losses of efficiency of the X-ray bulb, so far as 

 possible. The exhaustion was made during the exposure, which was 

 always brief. At the distance D = 6 meters from the bulb, there is a 

 terminal corona at dp = 22 cm.; at D=i meter it appears a little later 

 at dp = 2$. (See Chapter II, figs. 24 and 25.) In fig. 45 the correspond- 

 ing points are joined by straight lines, for convenience. 



60. The same, continued. Discussion. Experiments of the present 

 kind are hampered by two annoying difficulties, the first being the 

 variability of the X-ray bulb, the other the tendency of the wooden fog 

 chambers to develop slight leaks which often pass unobserved. True, 

 the chamber is tested by a second exhaustion after each of the coronas 

 measured; but the unfiltered atmosphere entering anywhere is liable to 



