166 



C. Bams — Measurement of Fog Particles. 



(chromatic aberration) vanish after long standing and they are 

 particularly vivid immediately after falling. It was not even 

 now possible, in spite of all precautions in tipping the vessel, to 

 obtain an abundant crop of drops at pleasure. 



If the results are given graphically in a chart in comparison 

 with the computed data of my earlier experiments* as well as 

 with my later f experiments, the observed results lie below the 



H 





3 S i_ 

















1% 





\ \ 

 \ \ 

















10 





\ ° 



\ 















8 





\ ° 



\ 



\ 



— o — ■ 















6 







\ 

 \ 



O N 













4 







\ 



o 



\° G 



i 



> 



* 



4 







8 



dxiOm 

 Us 









■"-*—- __^___^ 





r-a 

























10 1Z 



ft 



latter where adiabatic conditions were assumed, and above the 

 more recent experiments where the effect of the successive 

 expansions was computed isothermally. In other words, the 

 observed diameters were intermediate but nearer the older 

 results. 



5. Number of droplets. — The following results were obtained 

 with the definite form of apparatus shown in figure 1. A 

 method of estimating the nucleation from a direct count made 

 under the microscope is obtained as follows : Let the plate s 

 be rotated to s' so as to catch the descending fog particles for 

 a definite interval of time, t. If v be their velocity, of subsi- 

 dence, all particles within a height, h, will be caught, if 



h = vt (1) 



and v = 10 6 ^ 2 /3*24 (2) 



where the usual value of the viscosity of air has been inserted. 

 Furthermore, m grams are precipitated per cub. cm. by the 

 given exhaustion, and if n be the nucleation 



n = 6m/ird* (3) 



* Phil. Mag. (6), iv, p. 24, 1902. See curve b in the following chart, 

 f This Journal (4), xvi, p. 325, 1903. See curve a in the following chart. 



