DISTRIBUTION WITHIN FOG CHAMBER. 3 



air. As the aluminum tube was carefully sealed (ground screw plug and 

 wax) the beta- and gamma-rays are here alone in question, and as the 

 bottom of the fog chamber through which the radiation passes may be 

 1 cm. thick and the walls are everywhere more than 0.2 cm. thick, only 

 the more penetrating beta-rays are active to reenforce the gamma-rays. 

 In fact the earlier work showed that the rays after passing 1 cm. of lead 

 produced an amount of nucleation only 30 per cent less than in the 

 absence of the dense barrier. Thus the whole phenomenon is practically 

 a question of the intensity of the gamma-rays. 



In the course of the work, curiously enough a number of contradictory 

 conclusions were reached, and it will therefore be advisable to report the 

 results chronologically, beginning with the data for low pressure differ- 

 ences. 



Table i. Distribution of nucleation within the glass fog chamber (43 cm. long, 14 

 cm. in diameter); nucleator, radium in thin aluminum tube. dp= 21 cm. Radium 

 atDcm. from end, axially without. Lines of sight (two goniometers, s l and s 2 ) 15 

 cm. and 35 cm. from end nearest radium, or 20 cm. apart. 



.V, x 10- 3 



19 

 14 

 17 

 17 

 19 



7 

 6 

 8 

 3 

 5 

 4 

 o 



IO" 



xA'. 



16 

 1 1 



17 

 21 

 16 



7 

 7 

 9 

 3 

 5 

 4 

 o 



Mean < \ T ' 



I ;N 2 



17,200 

 16,200 



7,000 

 8,000 



4,000 

 4,000 



Per 

 cent. 



100 



45 



24 



2. Data. The cylindrical glass fog chamber (fig. 1), rigorously free 

 from leakage, was placed, with its axis horizontal, in such a way that a 

 prolongation of the latter intersected the radium tube at a distance, D. 

 Two goniometers with their lines of sight about 20 cm. apart, and 15 and 

 35 cm. from the end (bottom) of the fog chamber nearest the radium 

 tube, were used nearly at the same time for the measurement of the 

 apertures of the coronas seen along the axis. Both were placed with the 

 pins nearly contiguous to the walls of the cylinder, so that the eye was 

 at a minimum distance of 30 cm. off. All the phenomena may in this 

 case be more clearly observed and the small coronas are less liable to drop 

 out before the measurement has been completed. The source of light 



