method. The actual micrometric measurements which have been made of these satellites with the largest telescopes give results which vary considerably among themselves. Hence the interest in trying the interferometer method. The apparatus used was similar to that shown in Fig. 103, i. e., it consisted of two movable slits in front of the objective of the eleven-inch glass at the Lick Observatory.

The atmospheric conditions at Mount Hamilton while the work was in progress were not altogether favorable, so thatFIG. 103 out of the three weeks' sojourn there there were only four nights which were good enough to use, though one of these nights was almost perfect; and on this one night most of the measurements were made. The results obtained, together with those of four determinations which have been made by the ordinary micrometer method, using the largest telescopes available, are given in the following table:

The numbers in the column marked A. A. M. are the results in seconds of arc obtained by the interference method. The other columns contain the results obtained by the ordinary method by Engelmann, Struve, Hough, and Burnham