276 



Kadium present in fog-chamber &p = 1S.5 



Kadium removed. 3.5 hours after removal, 21 



•21 " " 22 



29 23 



On leaving the fog-chamber for hours with- 

 out interference, the fog-limit for the excited 

 activity was found to be lower, the coronas 

 (cajt. par.) larger than if but a few minutes 

 elapse between the condensations. Thus it 

 takes time for the induced activity to saturate 

 the air within the fog-chamber with nuclei, 

 and more time as its activity is weaker. Per- 

 sistence in case of the larger (X-ray) nuclei 

 must be reckoned in houi's. 



A little induced activity was obtained 

 through the hermetically sealed glass tube 

 (walls say .5 millimeter thick) vanishing com- 

 pletely in about fifteen minutes, to the fog- 

 limit of dust-free air. The same radium in 

 the hermetically sealed aluminum tube (walls 

 say .1 millimeter thick) left an excited activ- 

 ity behind in the fog-chamber, vanishing in 

 about forty hours gradually to the fog-limit 

 of dust-free air. It seems, therefore, as if 

 something besides beta and gamma rays passed 

 through these relatively thick tubes. Leaving 

 this for further examination* I need merely 

 instance here the adaptability and sensitive- 

 ness of the condensation method for the pres- 

 ent purposes, where, moreover, the coronas 

 will indicate the numbers of nuclei produced 

 under any given conditions. 



2. The general facts of the preceding para- 

 graph are inferred objectively if an X-ray 

 bulb is placed near one end of a long con- 

 densation chamber of waxed wood and the 

 effect of sudden exhaustion viewed broadside 

 through plate glass windows.^ The coronas 

 obtained after short exposure are all roundish, 

 but taper in diameter from a large size near 

 the bulb to a vanishing diameter (apex) near 

 the middle of the chamber, with all inter- 



* An important question is here confronted: 

 Can an induced activity having any period of de- 

 cay (within limits) be produced by successive 

 filtering of the contents of the sealed tube con- 

 taining radium, through walls of difTercnt thick- 

 ness of density. In such a case the induced ac- 

 tivity (supposing that no emanation escapes) 

 would be a kind of phosphorescence. 



^Am. Jfnunal, Vol. 10, February, p. 175, 1905. 



[N. S. Vol. XXI. No. 529. 



mediate gradations of ajierture in correspond- . 

 ing intermediate positions. All lie within 

 two oblique lines symmetrically inclined to 

 the horizontal axis and meeting near the 

 middle. The pressure difference used is thus 

 more and more in excess of the fog-limit as 

 the line of sight is nearer the bulb. Beyond 

 the apex, the pressure difference used is be- 

 low the fog-limit. The number of nuclei 

 within the given range of condensation, i. e., 

 above a certain lower limit of diameter, in- 

 creases with the intensity of the ionization. 

 Smaller nuclei occur throughout the chamber 

 and particularly within the reentrant region 

 left blank after condensation. 



3. If the number of nuclei (n per cu. cm.) 

 is mapped out in relation to the correspond- 

 ing pressure difference, 8p. the initial slopes of 

 the curves obtained are steeper as the fog- 

 limit is lower. Thus per increment of Bp of 

 one cm. of mercury above the fog-limit of the 

 ionized medium, and decidedly below the fog- 

 limit of dust-free air, I observed with 



Radium in sealed aluminum tube within fog-chamber, 



a>i = 12,000 



Radium in sealed glass tube within fog-chamber. 6,000 

 Radium in sealed glass tube, 45 cm. from fog- 

 chamber, outside 4,000 



Do., 200 cm. Irom fog-chamber 1,000 



Dust-free air {Sp above 24.5 cm., radium at in- 

 finity ) 4,000 



Hence, effectively, the gradation of nuclei is 

 more even, finer, i. e., with fewer gaps, as the 

 fog-limit is low and the maximum size of 

 nucleus larger; while for sparse distributions 

 the steps from one nucleus to the next in the 

 order of average size are relatively large. For 

 a different medium, dust-free air, for instance, 

 the gradation is characteristically different. 



Carl Bar us. 



Brown University, R. I. 



CURRENT NOTES ON METEOROLOGY. 



LONDON FOG INQUIRY, 1901-3. 



The ' Report of the Meteorological Council 

 upon an Inquiry into the Occurrence and 

 Distribution of Fogs in the London Area, 

 during the Winters of 1901-2 and 1902-3' 

 has been issued, and is summarized in Nature 

 for January 12, 1905. The investigation was 

 carried on with the aid of the Metropolitan 



SCIENCE. 



