C. Hants — Measurement of Fog Particles. 



167 



Finally if c is the area of the field seen in the microscope and 

 n' the number of particles falling into this field 



n' — nhc (4) 



From these equations n is obtained by eliminating v as 



s -_ 2-UXn' 

 y n ~~tcm^W 



The values of the constants usually adopted were t = 30 sec, 



g =144X10- 6 sq. cm., ra 3 / 3 =2-8xl0~ 4 , whence tyn=l'75Xn'- 

 The experiments to test this method often gave serviceable 

 results some of which are inserted in the following tables ; but 

 at times the ^-values are out of proportion The reason of 

 this is three-fold : In the first place n is found from n l/s with 

 the usual difficulty. Again, in a simple arrangement like the 

 above, air currents cannot be quite excluded. They may arise 

 incidentally in the apparatus, or the motion of the plate even, 



Table I. — Observed diameters (d) of cloud particles and numbers (n) per 

 cub. cm. m=4*7xl0 -6 g per cub. cm.; micrometer factor '00004 cm . 

 Distances of goniometer and light from condensation chamber, 85 cm and 

 250 cm ; chord s for radius 30 cm . Exhaustion to dp=17 cm . 















n ob- 



n com- 



d ob- 



d com- 





s 



corona. 



cxlO 6 t 



n' 



served. 



puted. 



served. 



puted. 





cm. 





cm. 2 



sec. 









cm. 



cm. 





- - — - 



olive 



140 



30 



37 



270000 



250000 



. _ _ _ 









6-0 



wrg 



140 



30 



27 



105000 



90000 











Phosphorus 



10'2 



wobg' 



70 



30 



17 



210000 



210000 



•00036 



•00036 



nuclei 



7'4 



w pbg 



70 



15 



6 



. _ _ . 



. - . » 



48 



41 





7-1 



w'bp 



















. 



56 



42 





4-7 



corona 





-- 













80 



61 



Air Nuclei 



45 



corona 



140 



15 



9 



30000 



40000 



•00064 



6-5 



g'bp 



_ _ . 



_ 



_ _ 



_ — - - 



.... 



52 



8-1 



wcbg' 



70 



15 



14 



120000 



150000 



48 



8-2 



Do. 



70 



15 



16 



180000 



150000 







Particles as small as -0003 cm present throughout. 



"Do] 6*5 gbp 140 15 10 43000 100000 '00064 '00046 



6-5 g'bp .... 56 46 



Particles graded as usual. 



•00064 

 46 

 39 

 39 



Particles graded as usual. 



if parallel to itself, may stir the air unless some form of guard 

 ring attachment is added. Particles are thus swept down 



