50 A CONTINUOUS RECORD OF ATMOSPHERIC NUCLEATION. 



the slow diffusion and consequent absence of homogeneous vapor. I hope, 

 however, by keeping the drum in rotation arotind the axis of vision, as already 

 suggested, to counteract this discrepancy, and correspondingly to prolong the 

 series. 



5. Carbon disulphide. The vapor of this reagent is another in which 

 coarse normal coronas usually appear. The endeavor to produce the higher 

 coronas with sulphur, punk, or air nuclei fails if the pressure differences are of 

 the same order as those used for water. Particles of the fog are usually about 

 d=.ooi cm. in diameter for strong nucleation, and the strong coronas produced 

 on shaking showed diameters of the order of d = .0015 under the given conditions 

 of exhaustion. Relatively large coronas were obtained with nuclei which 

 apparently rise from this reagent spontaneously. Thus after about 2 hours 

 d=.oo2, after 6 to 15 hours d=.ooi2 cm. was observed. The fact that the 

 coronas increase in size in the lapse of time suggests other explanations than the 

 slow diffusion of vapor or the difficulty in keeping it uniformly saturated when 

 successive exhaustions are made. For in this case coronas would decrease and 

 the size of particles increase, whereas the reverse is observed. 



The computation of the number of nuclei per cubic centimeter for carbon 

 disulphide is more precarious in view of the high vapor pressures and the de- 

 ficiency of data applying throughout the range of temperatures involved. For 

 the case of a pressure decrement of tf/>=i8 cm., from 76 cm., and at 20, the 

 adiabatic fall of temperature would be as far as 34, the rise thereafter due to 

 condensed liquid as far as 5. This implies 53Xio" 6 grams of moisture per 

 cubic centimeter, whence with the above goniometer the number of nuclei per 

 cubic centimeter would be ^ = 34 (io5) 3 = .io/(iod) 3 . 



The coronas obtained by spontaneous nucleation thus correspond to 

 n= 13,000 after 3 hours and n = 50,000 after 6 hours or more. Finally, punk 

 nuclei after two or three exhaustions with shaking were still present to the 

 number of n 75,000 per cubic centimeter. 



