88 Barus — Geometric Sequences of the Coronas of Cloudy 



after many exhaustions from fatigued elasticity. I shall here 

 quote results for the double drum only. This was about 180 cm 

 long and 30 cm in equatorial diameter, carefully blackened 

 within to prevent reflection from the sides ; for all coronas are 

 advantageously projected against a dull black background. It 

 was made of copper and external ribs obviated collapse. The 

 Welsbach flame is placed at one end, the eye at the other, with 

 appurtenances close at hand for exhaustion and filtration. The 

 end windows were 5 cm in diameter. When the axial color is 

 specially to be observed it is best to remove the screen from 

 the mantle and to look at the full extent of the mantle. 

 Ground glass covering the window and illuminated by sun- 

 light is preferable. As these colors are seen mixed with the 

 intense glare of white light, they vanish long before the coronas, 

 and a drum 5 or 10 meters in length will eventually be neces- 

 sary. With each exhaustion all the preceding colors for 

 smaller water particles are flashed through until the tint hovers 

 over the most advanced of the colors. After this there is a 

 tendency to a retrograde movement, but it soon vanishes. The 

 same difficulty of making observations on these fleeting color 

 contrasts obtains here as above. 



The yellows and browns of the first order, which can be pro- 

 duced so splendidly in the steam tube, were not obtained here 

 except perhaps as a retrogression from the blues. The other 

 colors are given in Table III on a plan identical with Table I. 

 Two independent series are shown with the coronal and axial 

 colors of each. The exhaustions are necessarily kept low, 

 which, however, is an advantage, as a more finely graded 

 sequence of colors is obtained. If J ^=l0 nil+bt)logy as in para- 

 graph 4, y =y/p = -888, and yV? = '919. The constant b 

 was specially determined and found to be b — *092, agreeing 

 sufficiently with the above to admit of the same value in the 

 corrections. The data are omitted for brevity. 



The method of paragraph 5, for computing the actual num- 

 ber of nuclei, iT, between the adiabatic and the isothermal 

 numbers, JSf u W^ when extended to the double drum gives 

 for = 293°, p = 76 cm , p' = 68 cm , the absolute temperature 

 0'— 283-3°, as a first approximation. Inserting these data with 

 r = 582 and r' — 586 into the equation for entropy, the approx- 

 imate value 1 — a?' = "0243 grams of water precipitated per 

 gram of mixture results. This is equivalent to '204 cal. evolved 

 per gram of air by the precipitation of the available '0143 

 grams of moisture. The rise- of air temperature is thus '86°. 

 Hence the new data are 6 = 293°, 6 f = 284°, and these with 

 the above values of r and r' give 1—x' = *021 grams. Thus 

 361/10 9 grams of water are precipitated per cub. cm. of moist 

 air. If as before 5 X 10 4 nuclei are present per cub. cm. at the 



