V ol. 7, 1921 ASTRONOMY: MICHELSON AND PEASE 
143 
TABLE 1 
Constants for the Six Distances Given in Figure I for the "Pure Line" in Rat 
105 on the 25th Day of Blood Infection. The Means and Standard Deviations 
Are in Microns 
MEAN 
STANDARD 
DEVIATION 
COEFFICIENT OF 
VARIATION 
Post-Para 
4.268 ± .036 
. 544 + . 025 
12.74 + .61 
Para-Nuc 
10.854 + .016 
.240 ± .011 
2.21 + .10 
Nuc-Ant 
9.511 ± .047 
.704 ± .033 
7.41 + .35 
Ant- End 
6.619 ± .068 
1.010 + .048 
15.27 + .74 
T. Length 
31.251 + .059 
.875± .041 
2.80 + .13 
Width 
1.590 j: .015 
.230 + .010 
14.47 + .70 
1 This and a later report form a preliminary account of a se ries of investigations 
which are being carried out in this laboratory on variation and inhe ritance in T. lewisi. 
2 Throughout this work the term "pure line" infection has been used to designate an 
infection, the trypanosomes of which have all arisen from a single organism. A given 
"pure line" may either have been started from a single specimen or it may have been sub- 
inoculated from such an infection. 
3 See especially Jennings, H. S., Proc. American Phil. Soc, 47, 1908 (393-546). Amer- 
ican Nat., 43, 1909 (321-337). Ibid., 45, 1911 (79-89). 
MEASUREMENT OF THE DIAMETER OF ALPHA-ORIONIS 
BY THE INTERFEROMETER 
By A. A. Michklson and F. G. Pease 
Mount Wilson Observatory, Carnegie Institution of Washington 
Communicated March 12, 1921 
It was shown in these Proceedings 1 that in the application of inter- 
ference methods to astronomical measures, the fringes show no decrease 
in visibility with the slits separated by the full aperture of the 100-inch 
Hooker telescope even when the seeing is poor. It was therefore decided 
to build an interferometer with movable outer mirrors in order to test for 
separations as great as 20 feet. 
The interferometer bed consists of a fabricated steel beam, designed 
with special regard to lightness and stiffness, mounted on the end of the 
Cassegrain cage of the 100-inch reflector (fig. 1). Two tracks were 
planed on the top, true to 0.001 inch (0.025 mm.), the frame being 
supported on the planer as it was to be mounted on the telescope. On this 
beam are mounted four slides, each carrying a mirror about 6 inches (152 
mm.) in diameter, inclined 45 degrees to the base. The two inner mirrors 
M 2 , M 3 , are fixed, 45 inches (114.2 cm.) apart, while those of the outer pair 
Mi, Mi, are movable and can be separated to a distance of 20 feet (6.1 m.). 
The light pencils are reflected from the outer to the inner mirrors, thence 
over the customary path a, b, c, d, in the telescope, and are viewed with an 
eyepiece at the Cassegrain focus d, where the equivalent focal length is 134 
