C. Barus — Coronas with Mercury Light. 75 



here. If y is the exhaustion ratio, the nucleation n z of the 

 2th exhaustion in terms of the original nucleation n will be 



n, = n.y(i-,s/0(i-s/0 — -(i-*/**-) 



where S is a subsidence constant and s the chord of the 

 angular diameter of the coronal disc on a radius of 30 cm . 



To find jS, two consecutive values of s suffice, or 



S=s z *(l-s z 3 +1 /ys z 3 ) 



approximately. The diameter of particles, d, is in terms of n, 



d 3 = 6m/irn 



If X = 54*6 X 10~ 6 cm. is the wave length of green mercury 

 light and 6 the angular radius of the first green minimum of 

 the coronas 



sin 0=-61 X/ (d r /2). Since sin 6 = s / 2JR, 



R being the radius of the goniometer of which s is the chord, 

 d' the diameter of fog particle (the primes referring to optic 

 measurements) 



d'= -004 /s 

 for mercury light. Hence, optically, the nucleation 



1(T 6 n' = 29-8 ms\ 

 where m grams of water are precipitated per cubic centimeter 

 on exhaustion, and found in the exhausted fog chamber. 



4. Data with green mercury light, 10 6 \ = 54'6 cm . — Omitting 

 the correlative data with white light and removing all tables 

 for lack of space, the charts figure 1 contain results obtained 

 with a mercury arc lamp as the source of light. Different 

 annuli are measured and the chords, s, on a radius of 30 cm are 

 distinguished by accents, as follows : 



s f is the chord of the green disc, 



s" is the chord of the inner edge of the first green ring, 



s" r is the chord of the outer edge of the first green ring. 



The edges are fairly sharp. Hence 

 s- (s' + s")/2 



may be taken as the chord of the first green minimum. Optic- 

 ally the diameter of the particle is then d' — '004/5. 



The water precipitated per cubic centimeter, m, differs with 

 the drop of pressure, $p 9 /p, and the temperature. In the suc- 

 cessive parts of the chart the data are 



Parts I, II, 10 8 ?n=4-l grams, »'=122 s 3 (omitted) 



Parts III, IV, =4*12 grams, ^' = 123 s 3 



Parts V-VIII, =4-02 grams, n' = 120 s 3 



