THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. YI. — On Geometric Sequences of the Coronas of Cloudy 

 Condensation, and on the Contrast of Axial and Coronal 

 Colors ;* by C. Barus. 



Introductory. 



1. The object of the following paper is, in the first place, to 

 map out the sequence of coronas in case of water vapor, in 

 terms of the numbers of particles producing them, relatively. 

 The extreme diversity of coronal display seen in moist nucle- 

 ated air lends itself well to a geometric method of classifica- 

 tion when the colors are produced by successive exhaustions. 

 The classification is thus primarily suggested by experiment. 

 ^In .the second place, I shall make certain theoretic deduc- 

 tions from the time losses of nuclei observed, which clear up 

 some moot points left in abeyance in my earlier experiments 

 on the same subject. 



I purpose in the third place to contrast the color of the cen- 

 tral patch of the coronas with the axial colors seen in the 

 steam jet, or under like circumstances with even greater satura- 

 tion, in the adiabatically exhausted drum. The coronas must 

 in large measure be diffraction phenomena ; the axial colors 

 cannot be so explained, but are evoked by some unknown kind 

 of absorption. The contrast is sharply brought out by the 

 experiments. 



Finally I shall make an estimate of the absolute dimensions 

 of the water particles in action and of their number and indi- 

 cate a method which I am pursuing in a quest for definite abso- 

 lute results. 



2. Apparatus. — In my first experiments tubular apparatus 

 was used in great variety ; but in these instances the colors are 



*The researches outlined in the present paper are encouraged by a grant from 

 the Smithsonian Institution. Here I can only acknowledge my indebtedness to 

 Secretary Langley, for his patience and confidence. 



A.M. Jottr. Sci. — Fourth Series, Yol. XIII, No. 74.— February, 1902. 



