60 A CONTINUOUS RECORD OF ATMOSPHERIC NUCLEATION.* 



corona is particularly characteristic, consisting of three broad color bands. 

 The disc is green with the Welsbach lamp. 



III. w vp b g' r'; w g b p; w yo (b) gb r; w r (b) g r'. 



The next series (IV) is a variation of w r' b g r, approaching the steady 

 normal coronas of the next cycle. The colors are very closely packed together, 

 so that it is difficult to produce definite types of them at will. Very small 

 differences of diameter of cloud particle materially change the details of the 

 color scheme. Incidentally, however, the "green" corona, wg' b p is obtained 

 particularly with the Welsbach lamp; the red of the first ring changes from 

 y' to br'. w r | g is frequent. 



In succeeding coronas the normal type is practically permanent and the 

 observable variation is merely in diameter. 



4. Apertures. For the measurement of the relative apertures (s) of the 

 coronas the inner edge of the first ring or the diameter of the white patch is 

 unsuitable, because this demarcation is usually vague. On the other hand, the 

 demarcation between the first and second color rings is usually very sharp 

 and the colors in contrast. Most of the measurements have therefore been 

 made to the outer edge of the first ring. Naturally there will be periodi- 

 city from the fluctuation of wave length specified, but this periodicity per- 

 sists when homogeneous light is employed. Unfortunately, the coronas are 

 usually so faint that the simple means for homogeneous light are not available 

 and electric or sunlight must be employed. For practical purposes, colored 

 annuli are thus inevitable. 



The opalescent colors of the series marked II above soon fade. Evapora- 

 tion takes place while the partially exhausted air is regaining its original tem- 

 perature. Particles become irregular with no markedly preponderating size. 

 Initial coronas are fleeting, final coronas washed. The evaporation effect is 

 much less evident in Series III and the succeeding series. 



DATA OBTAINED WITH THE WELSBACH BURNER. 



5. Explanation of tables. To correlate the present with my earlier in- 

 vestigations I will give a series of results found by using a small circular part of 

 the Welsbach mantel as a source of light. Coronas in this case are more easily 

 identified because of the simplified color scheme, to the practical advantages of 

 which I have already referred. 



In table i, z denotes the number of the partial exhaustions each of volume 

 ratio, y, and made in succession, t, the current time in minutes (the interval 

 being about 3 minutes to allow for adjustments and for diffusion), 5 the chord 

 of the angular radius, <p, at radius R, so that s/R = 2 sm</-. The eye and source 

 of light were at distances 85 and 250 cm. from the intervening condensation 

 chamber, and the former was focussed for long distances. The pressure and 

 temperature of the atmosphere were P and 6, and the fixed pressure decrement 



