84 CONDENSATION OF VAPOR AS INDUCED BY NUCLEI AND IONS. 



DISTRIBUTIONS OF VAPOR NUCLEI AND OF IONS IN DUST-FREE 



WET AIR. 



53. Behavior of different samples of radium. New fog chamber. 



It was my hope to be able to obviate the need of using the trouble- 

 some and inconstant X-ray bulb by replacing it by a strong sample of 

 radium. It also seemed possible that the fog chamber might be stand- 

 ardized in this way; but the attempts proved quite abortive, as indeed 

 might have been expected. The coronas were but slightly increased on 

 intensifying the original activity of radium I, 100 nig. io,oooX , equiva- 

 lent to say io 6 , by adding radium II, 10 mg. 2oo,oooX, equivalent to 

 2Xio 6 ; radium III, 100 mg. io,oooX, equivalent to iXio 6 ; radium 

 IV, 100 mg. io, ooo X , equivalent to i X io 6 ; radium V, 100 mg. 20,000 X , 

 equivalent to 2Xio 6 ; on the whole, therefore, about seven times. 

 Obviously the radium must be kept sealed in tubes of aluminum or of 

 very thin glass, as otherwise the fog chamber would become infected, 

 which would be fatal to experiments of the present character. 



The reason of the relative inefficiency of the radium is given by the 

 equation dn/dt = a bn 2 , where a is the number of ions generated per 

 second and bn 2 the number which decay per second. Hence for the 

 case of equilibrium a/b = n 2 , where a varies as the activity of the radium. 



If the five samples in question be taken together, therefore, the 

 equilibrium nucleation n would be, for any fixed distance of the radium 

 from the fog chamber, 



Now, n varies as S 3 (if 5 be the angular diameter of the coronas) in a 

 general way, and therefore the resultant 



a (X. S 6 



Consequently enormous increases of the nucleation bring about but 

 slight changes of the angular diameter of the coronas. This estimate 

 is not quite correct if the values of b vary, as seems to be the case, with 

 the nucleation; but for the larger nucleations here in question such 

 an effect is not observable. If it can be controlled a new method of 

 standardizing the fog chamber for moderate coronas would be suggested. 



54. Data Results of this character are given in table 37, where 5 is 

 the double tangent of the corona on a radius of 250 cm., n the nucleation 

 corrected for the exhaustion v 1 /v = i.28f. In addition to the effect 

 of aggregating the radium tubes, their position on the outside of the 

 fog chamber is indicated as follows: a denotes that the tubes are placed 

 on the outside of the walls of the horizontal glass cylinder, above its 

 middle or equatorial parts; b that they are similarly placed near the 

 brass cap at the exhaust end; c that they are placed near the remote 



