AIR ENERGIZED BY X-RAYS. 41 



The new data are, in fact, quite different from the old. After intro- 

 ducing the sealed radium tube the nucleation rises rapidly to a maxi- 

 mum, falling off, however, to a mean value in 14 hours. On removing 

 the radium tube from the chamber, the nucleation falls off at once to 

 about 10 per cent of its original value. This appreciably increases a 

 little at first, but vanishes practically in the ensuing 12 hours. One 

 may note that the second and subsequent exhaustion usually show 

 smaller nucleations than the first, as though it were possible to reduce 

 the nucleation faster than it is restored. It is probable therefore that 

 in the first experiments something like an emanation escaped from the 

 ground joint or that the outside of the aluminum tube had become 

 radio-active during filling. Nevertheless, a residual effect is in evidence 

 in the last experiments made, which can not be explained away. 

 Something has escaped through the aluminum tube which produced 

 the lingering radio-activity of the chamber (fig, 37). 



EXPERIMENTS WITH DUST-FREE AIR ENERGIZED BY THE X-RAYS. 



37. Persistence of nuclei produced by X-rays in the lapse of time. The 

 nuclei produced by the X-rays of sufficient intensity (i. e., when the 

 bulb is near the fog chamber), if left without interference, are indefi- 

 nitely persistent as compared with the initial ionization. Table 23 

 shows some incidental results. It is not possible to determine the 

 law of decay (probably exponential) by this method, as the nuclei are 

 lost or otherwise destroyed by the condensation which determines their 

 number. The initial nucleation must therefore be inferred. Again, 

 the first coronas (if the X-ray bulb is at one end of the fog chamber as 

 was here the case) are apt to be distorted, so that the corona obtained 

 on first exhaustion is not available for definite measurement. To some 

 extent the datum is supplied by the corona of the second exhaustion 

 (s 2 ), observed after the fog particles of the first corona (s^ have sub- 

 sided, filtered air slowly replacing the exhausted air. m refers to 

 the precipitation of water per cubic centimeter, at the pressure 

 differences shown by the subscripts. 



Within an hour or more after the exposure the coronas are invari- 

 ably strong. Within 16 minutes, 36 minutes, even 85 minutes, they 

 show diminutions of aperture comparable with that usually observed 

 in the case of other nuclei. In half an hour the nucleation has not 

 fallen below }4, in an hour not below #, etc. After 4 hours, however, 

 all nuclei within the scope of the exhaustion have vanished. 



