Vol. 6, 1920 
PHYSICS: A. A. MICHELSON 
475 
diameter of some of the larger stars in the manner set forth in the Philo- 
sophical Magazine for July 1890, a trial was made at the Yerkes Observa- 
tory using two apertures in front of the 40-in. refractor. 
The interference fringes at the focus remained fairly steady, with "seeing"^ 
only 2 to 3 on a scale of 5. 
On invitation of Dr. George E. Hale the test was repeated with the same 
success with the 60-in. reflector. 
With the 100-in. reflector the interference fringes were produced by a 
modification consisting in placing the screen with the two apertures at 
a short distance from the focus, which made the control of the distance 
between them and their position angle much easier. The interference 
fringes were again fairly steady, even when with "seeing" but 2 on a scale 
of 10, and consequently very considerable "boiling" of the images under 
the high magnification necessary (2000 to 3000 diameters) . 
The following is a resume of observation of Capella by J. A. Anderson, 
showing that measurements may be obtained with an error of but a few 
ten-thousandths of a second of arc. 
STATBME:NT of RKSUI.TS FROM OBSERVATIONS OF CapEIv1.A WITH THE MiCHElvSON 
Interferometer Apparatus 
DATE OP OBSERVATION 
POSITION ANGIvE 
DISTANCE 
Dec. 30, 1919 
148°. 0 
0".0418 
Feb. 13, 1920 
5.0 
0 . 0458 
Feb. 14, 1920 
1.0 
0.0451 
Feb. 15, 1920 
356.4 
0.0443 
Mar. 15, 1920 
242.0 
0.0505 
The constants of the apparent ellipse fitting these observations are as 
follows : 
Semi-major axis 0".0511 
Semi-minor axis 0 . 04 1 7 
Position angle of major-axis 49° .2 
The spectroscopic orbit being practically a circle {e = 0.016) the angle 
between the orbit plane, and the tangent plane to the celestial sphere is 
35° (or better 145°, since motion is retrograde). 
Parallax of Capella a little under 0".050. 
Preparations are now under way at Mt. Wilson for testing the possi- 
bilities of the interferometer method with a base of 18 to 20 feet. 
Further details will appear in the Astrophysical Journal. 
