72 NUCLEATION OF THE UN CONTAMINATED ATMOSPHERE. 



the return series inferior, superior, and mean coronas occur together. 

 It would be difficult to conjecture any reason for the apparent mini- 

 mum at Z?=5o cm. and the apparent maximum at Z?=2oo cm., and 

 they will presently be shown to be referable to the bulb. In any case, 

 however, the mean decrement of nucleation within 6 meters is certainly 

 less than one-fourth, evidencing an astonishingly small distance effect. 



TABLE 44. Nucleating effect of X-radiation from different distances ; Sj> = 25 cm. 

 Time of exposure, i min., prolonged through condensation. 



*7 cells in remaining experiments, 

 f i minute after exposure. 



\ Taken but not recorded. 



To guard against variations of the tube, the abbreviated series were 

 made as given in the second, third, and fourth parts of the table (upper 

 curves 69); and these show what was to be expected from the prelimi- 

 nary results, that within the 6 meters of observation about the same 

 nucleation is produced in the fog chamber (r^/. par.} irrespective of 

 distance. Finally, part V of the table proves that the apparent mini- 

 mum at )= 50 cm. is an error. 



The absence of a distance effect in the case of the nonincased 

 wooden fog chamber is astonishing and implies that the space within 

 the 6 meters of observation is everywhere equally full of the nucleus- 

 producing radiation. This behavior, moreover, is different from the 

 fluorescent, photographic, or even the electrical effect of the X-rays. 

 Thus the phosphorescent screen is intensely illuminated at >=5 cm., 

 while at 2 meters it is very dim and at 6 meters quite dark. It is nat- 

 ural to infer that the constancy of radiation is due to atomic disinte- 

 gration of the platinum auticathode, when bombarded by the cathode 



