52 NUCLEATION OF THE UNCONT AMINATED ATMOSPHERE. 



the exposure to the radiation before the observation was taken. The 

 resulting apertures are thus reduced, about two-thirds of the nuclea- 

 tion having vanished ; but they are otherwise comparable and much 

 smoother than in the absence of a lapse of time, L, between the end 

 of the exposure and the condensation. Two successive exhaustions 

 are often made for the same exposure, for which A^ and N 2 are the 

 nucleations reduced to air at normal pressure. 



TABLE 30. Fog limit and effect of pressure difference for combined filter and wet- 

 sponge tube. Dust-free air energized by X-rays. Observation after lapse of about 

 30 seconds. 



* Air nuclei. \ Nonenergized air. * Lapse, 3 min. \\ Lapse, 30 sec. 



t Accidental delay. Same as air not energized, ft Lapse, o min. 



In the first part of the table (curves 52, 53), while the values of s\ 

 and s 2 reach a limit, the uucleations N\ and N z continually increase 

 and are about N~ 25,000 apart throughout the whole range 8^ = 25 

 to 41 cm. N l shows the number of nuclei left in dust-free air about 

 half a minute after exposure to the X-rays ; N% presents the case of 

 dust- free air. 



The second part of the table is irregular. The mean curves, how- 

 ever, preserve the same relations at first, the nucleations of the ener- 

 gized air being 25,000 in excess. Toward the end of the curves both 

 the energized and nonenergized air show apparently decreased nuclea- 

 tion, while the former falls to the low values due to the normal air 

 nucleialone. The X-ray excess has been quite wiped out at 



