7 6 



NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



cm. in thickness is more than sufficient to reduce the nucleation one- 

 half. Thereafter the remaining thicknesses up to i cm. or more does 

 not reduce it further. A close comparison is given at the end of the 

 work, in which N=j6,ooo falls off to -^=32,000 for 6 plates, or a 

 thickness of about 0.84 cm. (curve 81). 



An interesting comparison is given for the efficiency of the X-ray 

 tube radiating from this distance either from the front face of the anti- 

 cathode or from the rear face of the anticathode, the tube in the latter 

 case being completely reversed (curve 80). The mean results are 

 respectively .^ = 42,500 and ^=34,600, showing the anticathode to 

 behave as if it were transparent or at least radiating from both 

 faces in all directions. Indeed, even if the anode and the cathode are 

 exchanged (reversed current), considerable radiation is sent out; as, 



for instance, 



Concave mirror the cathode, 7^ = 47,000, 



Concave mirror the anode, N- 



7,ooo, 



or about 16 per cent of the nucleation has been retained (curve 80). 

 The coronas obtained when lead screens are used in front of the fog 

 chamber are clear and often multi-annular, showing the nuclei to be 

 very nearly of a size. 



FIGS. 79-82. Illustrating table 47. 

 In the above chart Tab. 20= present table 47. 



