Vol. 7, 1921 
ASTRONOMY: F. G. PEASE 
177 
2 Jeans, Dynamical Theory of Gases, p. 247. 
3 Adams, "The Quantum Theory," Bull. Nat. Res. Council, 1, No. 5, Oct., 1920. 
4 Jeans, loc. cit., p. 246. 
5 Ithaca, Physic. Rev., 14, p. 368. 
6 Wm. A. Felsing (Thesis), Technology Press, June, 1918. 
7 Keyes, loc. cit. 
*Proc. R. Soc. London, 84A, p. 595. 
9 Leipzig, Ann. Physik, 17A, 1882 (418). 
10 Proc. R. Soc. London, 87A, pp. 556-57. 
11 Phil. Trans. R. Soc, 185A, p. 572. 
12 J. Chem. Soc. London, 99, p. 708. 
13 Ann. Physik, 59, p. 200. 
^Landolt Bornstein (1912). 
15 Z. Anorg. Chem., 93, p. 18. 
16 Brillouin, Leqons sur la Viscosite, pp. 152-159. 
THE ANGULAR DIAMETER OF ALPHA BOOTIS BY THE 
INTERFEROMETER 
By F. G. Pease 
Mount Wilson Observatory, Carnegie Institution of Washington 
Communicated by G. E. Hale, May 2, 1921 
Since the measurement of the diameter of Betelgeuse 1 in December, 
1920, observations for the determination of stellar diameters have been 
continued with the 20-foot interferometer attached to the upper end of 
the 100-inch Hooker reflector. 
Several definite results have been obtained, and others, less definite 
because of poor observing conditions, have been partially checked by 
comparison with stars whose diameters are known to be too small for 
measurement with this instrument. Let the visibility of the zero fringes 
for any particular separation of the mirrors be reduced by seeing which is 
poor as compared with that on a fine night; it is then hopeless to make 
final measures. If, however, the interferometer is turned to a neighbor- 
ing check star and the fringes are seen, and then turned to the star under 
consideration and they do not appear, the observer is justified in saying 
that there is a definite decrease in visibility. 
The data thus far obtained are as follows: For a Tauri (Aldeberan) 
fringes of gradually decreasing visibility have been observed at 13, 14.5 
and 19 feet. Further observations are necessary between the last two 
positions to determine whether the fringes vanish between these points 
or whether a longer beam will be necessary to obtain a measure of the 
diameter. If the fringes vanish around 16-18 feet, as observations under 
poor conditions lead one to suspect they will, then the fringes observed 
at 19 feet must lie beyond the point of disappearance, on the ascending 
branch of the visibility curve where it rises toward the second maximum. 
