REGIONS OF MAXIMUM IONIZATION. 



43 



from infection such as an emanation would produce, and anything of 

 this kind is at once detected. 



35. Long fog chamber. After obtaining these results, the work was 

 resumed with the aid of a larger fog chamber, F F, fig. 12, conical in 

 shape, no cm. long, 22 cm. in diameter at the broad end, tapering down 

 to 14 cm. at the small end, E, whence the exhaustion took place. It was 

 so mounted as to place the axis slightly inclined above the horizontal, 

 in order that an even depth of water, w, from end to end, might be stored. 

 In the first experiments the large end was of glass, in the later of metal, 

 but this difference is without appreciable effect upon the present results. 

 In each case a hole H, 2 or 3 cm. in diameter, was available near the 

 center of the large end for the introduction of an axial aluminum tube 

 AR (walls o.i i cm. thick), running from end to end of the chamber and 

 closed at R within it. In the inside of this tube the sealed radium tube- 

 lets could be moved from place to place, in a way similar to the method 

 followed in the preceding experiments. No wet-cloth lining was intro- 

 duced, because the experiments had to be performed so slowly that 

 saturation in case of a clean fog chamber, to which water adheres in an 

 even film, was assured. The best method of cleaning is vigorous rubbing 

 with a soft rubber probang, as for instance, a thick piece of rubber tubing 

 at the end of a metal rod. Every part of the glass must be scoured. 



FIG. 12. Section of long fog chamber with hollow aluminum core. 



The chamber was too large to admit of the capture of as many ions for 

 like conditions of exhaustion as was the case with the preceding smaller 

 apparatus, but this difficiency is of no importance here. Filtered air is 

 admitted through 7. 



36. Data. Table 15 gives an example of typical results as obtained 

 both with the glass and the metal capped fog chamber, the opposite 

 (exhaustion) end being always of brass. In the first two parts of the 

 table the chamber was not quite tight, but the leak was sufficiently insig- 

 nificant to virtually filter the inflowing air, as was proved by the direct 

 experiments and by the third part of the table, where the adjustment 

 remained quite free from leak throughout. In the fourth part some 

 miscellaneous experiments are added. Naturally the greatest care was 

 taken to remove water nuclei. 



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