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'v OL. 7, 1921 ASTRONOMY: MICHELSON AND PEASE 143 TABLE 1 CONSTANTS FOR THE Six DIsTANcEs GIVEN IN FIGUR1 I FOR THE "PuRS LINs" IN RAT 105 ON TH13 25T DAY OF BLOOD INFaCTION. THs MaANS AND STANDARD DEvIATIONS ARs IN MICRONS MRAN Post-Para Para-Nuc Nuc-Ant Ant-End T. Length Width 4.268 + 10.854 + 9.511 + 6.619 + 31.251 + 1.590 + .036 .016 .047 .068 .059 .015 STANDARD DEVIATION .544 + .240 + .704 + 1.010 + .875 + .230 + .025 .011 .033 .048 .041 .010 COEFPICIENT OF VARIATION 12.74 + 2.21 + 7.41 + 15.27 + 2.80 + 14.47 + .61 .10 .35 .74 .13 .70 1This and a later report form a preliminary account of a series 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 subinoculated from such an infection. 3See especially Jennings, H. S., Proc. American Phil. Soc., 47, 1908 (393-546). American Nat., 43, 1909 (321-337). Ibid., 45, 1911 (79-89). MEASUREMENT OF THE DIAMETER OF ALPHA-ORIONIS BY THE INTERFEROMETER By A. A. MICHELSON AND F. G. PEASE MOUNT WILSON OBSERVATORY, CARNEGIE INSTITUTION OF WASHINGTON Communicated March 12, 1921 It was shown in these PROCESDINGS' that in the application of interference 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,