TEMPERATURE EFFECT CONCLUSION. 41 



whence it appears that the increment of $ and R may replace each 

 other. 



A small radius at a high temperature is as effective as a larger radius 

 at a low temperature #, and that is substantially what the above data 

 have brought out. Naturally the equation has been pushed beyond its 

 limits, for the meaning of T for particles not large as compared with 

 molecular dimensions is obscure; but it appears in other cases and is 

 probably true here that the suggestions of the equation are trustworthy 

 in a general way. Computing 



by the aid of the adiabatic equation we may write ioV = i9.5/?? 1 log 10 

 (Pr/PaJ where Iog 10 pr/P (X = o.8, and $ 1 r = 2/io 5 , nearly. But ^ = 262 

 if the gas is originally at temperature t 2o, whence r = y5/io 9 . Since 

 dr/r= ddi/$ lt an increment of the radius of but 0.038 under the 

 given conditions is equivalent to a rise of temperature of i C. of the air 

 within the fog chamber or to 2000 more available nuclei, according to 

 the above figure. 



22. Another suggestion. The increment of about 2000 nuclei per 

 degree of temperature under the conditions given may also be looked 

 on as a parallel to what occurs in case of a radiant field like that pro- 

 duced by the X-rays. One may regard ionization as a state of dissocia- 

 tion sufficiently advanced to set free electrons and from this point of 

 view equivalent to a very high degree of temperature. One may thus 

 expect a passage of the vapor nuclei of wet dust-free air into the ions 

 through a continuous gradation of nuclei, and may note that vapor 

 nuclei and ions always occur together. True, the latter have been 

 associated with the radiation penetrating the atmosphere, with good 

 reason, but the possibility of a collateral cause of the ionization within 

 the fog chamber may nevertheless be entertained. 



23. Conclusion. It is shown by direct observation that the number of 

 nuclei caught in dust-free wet air at low barometer pressure is greatly in 

 excess of the number caught (cast, par.) at high barometer. This result may 

 be accounted for as a necessary consequence of the thermo-dynamics of 

 the experiment, however large and unexpected the variations appear. 



The comparison of the nucleation of dust-free air with the cotempo- 

 raneous changes of atmospheric ionization shows no correspondence 

 whatever. This is curious, because the ions, though much fewer in 

 number, are larger in size than even the larger colloidal nuclei, and 

 therefore capture much of the moisture at low exhaustion. One must 

 conclude that the variations of the ionization are not sufficient to be 

 detected in the presence of the other nucleation. 



