7 8 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



TABLE 47, continued. Penetration of rays and reversal of tube, etc. 



* Taken, but not recorded. In the first two data the bulb is gaining strength. 



61. Apparent penetration of the X-rays coming: from 200 cm. and from 



6 to 1 cm. The results for D=ioo cm. are similar to the preceding. 

 It again takes less than one lead plate (thickness 0.14 cm.) to stop the 

 absorbable rays (curve 82). There is no extra thickness of lead as 

 an equivalent of the layer of 400 cm. of air removed. Again, about 

 one-half of the radiation is stopped by the first plate and greater thick- 

 nesses produce no further effect. At the end of the table a wall of 

 lead 1.7 cm. thick shows no additional absorption. Moreover, tinned 

 iron plate }4 mm. thick has no appreciable effect on the radiation 

 whatever (curve 82). 



The first experiments for Z? = 6 cm. show apparent previousuess of 

 the single lead plate (0.14 cm. thick); but this seems to be referable 

 to the intensity of the initial radiation without the lead screen, for in 

 the experiments at D = j cm., a single plate shows marked reduction 

 of the very large coronas observed. On the other hand, a plate even 

 i cm. thick absorbs very little of the radiation, for, roughly, about 80 

 per cent passes, in spite of the indefinite thickness of lead, between the 

 bulb and the fog chamber, completely screening off the latter. The 

 results throughout are curiously irregular and difficult to interpret, as 

 seems not unexpected, since all secondary radiators must now be close 

 at hand (curve 83). 



