EFFECT OF X-RAYS. 



53 



At the end of the table the preponderating effect of lapse of time 

 after exposure is indicated. All excess of nuclei is gone after 3 min- 

 utes, while the original excess of 83,000 is reduced almost two-thirds 

 in half a minute. 



46. Continued Rays not cut off during condensation. Table 31 

 (curves 54, 55) contains data for the coronal apertures obtained without 

 cutting off the radiation until after condensation has been produced. 

 The two minutes' interval of exposure is excessive (as the following 

 paragraphs show) when weak radiation (distance of X-ray bulb from 

 end of fog chamber, D = 150 cm.) is in question. The results in table 

 31 are distributed cyclically, and the return series shows less nuclea- 

 tion in general than the outgoing series. This is attributable to the 

 gradual temporary loss of efficiency of the X-ray bulb. Similarly the 

 fog limit is slightly below 20 cm. in the outgoing series and slightly 

 below 21 cm. in the return series, the rise being toward the nonener- 

 gized dust-free air (8/> = 24 cm.). 



TABLE 31. Fog limit and effect of pressure difference for combined filter and wet- 

 sponge tube. Dust-free air energized by X-rays. Bulb 150 cm. from end of fog 

 chamber. Exposure, 2 min. Observation taken during exposure, or lapse, o sec. 



In addition to this, the outgoing and the return series show a curi- 

 ous case of periodicity which may or may not be real ; but it is prob- 

 able that there is decreased nucleation after Bp exceeds 40 cm. The 

 initial increase of N with 8p is nearly straight and exceedingly rapid 

 (8Nj8p = 15,000, nearly). This is somewhat greater than the above 

 values for radium (about 12,000), but of the same order as the datum 

 for weak X-ray radiation. The corresponding data for dust-free 

 nonenergized air, given in the same chart, show that initially 

 SNI$p = 5,000, nearly, in correspondence with the earlier data so far as 

 can be made out. The nucleations N are throughout small as com- 

 pared with energized air, the excess in the latter case, if mean values 

 be taken, being of the order of 100,000 nuclei per cubic centimeter. 



