THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XXXIY. — The Apertures of Coronas, in Relation to the 

 Number of Nuclei and their Size • by C. Barus. 



1. Introductory. — Throughout my work with coronas, I 

 have relied chiefly upon the color sequences, and have taken 

 the data for numbers and sizes of cloud particles (a fixed degree 

 of supersaturation presupposed) from the tables given else- 

 where.* When apertures were measured this was done chiefly 

 for the identification of the series to which the corona belongs. 

 There is no doubt, however, that an expression for the diam- 

 eters of particles in terms of the aperture of the coronas would 

 be a great and immediate convenience, particularly as facility 

 in using the color sequences is apt to be lost, unless one is at 

 work with them continually. Apart from this the colors rep- 

 resent steps of progress, while the apertures should be con- 

 tinuously, even if irregularly, variable. The purpose is then 

 to find under what conditions the discrepancies of aperture 

 may be reduced to a minimum. 



If the supersaturation is constant throughout, the diameters 

 of cloud particles and their distance apart will in general be 

 proportional quantities. Let m be the grams of water pre- 

 cipitated, n the number of particles per cubic centimeter, 

 £> = n-V3 their distance apart, d the diameter of each, s the 

 aperture of the corona. If, therefore, for normal coronas d — 

 as, where a is a constant found by purely optical experiments, 



n=z(Gm/rra 5 )s 3 = ($m/7r)/d 3 = 1 / D\ and d= D (7r/6m)V3 



But it is doubtful if these equations are true even for normal 

 coronas, and they must certainly be a very crude approxima- 

 tes Journal (4), xiii, p. 81, 1902; Phil. Mag. (6), iv, p. 26, 1902; cf. 

 Structure of the Nucleus, Smithsonian Contributions, 1902, chapter 3. 



Am. Jour. Sci.— Fourth Series, Vol. XV, No. 89.— May, 1903. 

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