1898*

The class is well represented in Florida this winter by the Chandlers, Leggetts, Marcys, Bartletts, and by Lynch as a permanent resident.

The Popes are visiting their two married daughters near Chicago.

Mr. and Mrs. Seelman had a happy visit recently with the Leggetts at Scarsdale, New York.

Pete Adams out of a very busy life has kindly responded to the Secretary's request for an item about the 200-inch telescope.

IN THESE DAYS of a world at war it is remarkable to see the persistence of public interest in a great scientific undertaking like the construction of the 200-inch telescope in California. Requests for information regarding its progress and probable time of completion come by nearly every mail, often from countries as far apart as Sweden and Australia.

The instrument and optical shops of the Mount Wilson Observatory and the California Institute of Technology which have been engaged jointly upon this project are exceptionally well fitted for work upon specialized optical instruments, and so during the past year have been devoting much time to problems relating to national defense. Since the outbreak of the war essentially their entire activities and those of many members of the scientific staffs have centered about certain features of military equipment and design. Before this time, however, the massive mounting of the 200-inch telescope, weighing about 500 tons, was largely completed and erected in the steel dome, 135 feet in both height and diameter, which will house it permanently on Palomar Mountain about 90 miles from Mount Wilson. Remaining to be finished are some portions of the intricate driving mechanism which will enable the telescope to follow with great precision the apparent motions of the stars through the sky; but as at present erected it looks very much as it will appear in its final form.

The optical parts of the telescope are also well advanced. Two steps are necessary in bringing the 200-inch mirror to completion. The first is the accurate shaping, or figuring as opticians call the process, of the front face of the glass very closely to a concave spherical surface with a radius of about 111 feet. This has been finished and about five tons of glass were removed in the process. The second step is the very delicate one of transforming the spherical into a parabolic surface (the curve used in searchlight mirrors). This is necessary in order that all light from a star which falls upon the mirror may be condensed into a single point. At the center of the mirror the difference between the two curves amounts to only a small fraction of an inch, but such extreme care has to be taken to preserve uniformity and avoid depressions and elevations that the process is difficult and time-consuming. When the mirror is completed every point on its surface will lie within less than one five hundred thousandth of an inch of the correct curve. At present the surface is accurate to about one fifty thousandth of an inch.

When the telescope will be finally ready for use depends upon many factors, and wartime requirements may well delay its completion. An estimate of one to two years seems reasonable, however. It is interesting to realize that this great instrument will extend the frontiers of the observable universe to a distance at least twice as great as that to which man has attained in the course of his entire history.

Secretary, 57 Grove Hill Ave., Newtonville, Mass.