The observatory was one of the very first to be located on a site specially chosen for its adaptation to astronomical work, and its suc cess has had an important effect upon the sci ence of practical astronomy. No one would now ' think of locating a great observatory without careful consideration of the site to be occupied. The mountain observatories of the world owe much to the experiments made at Mount Hamilton.
The principal objects of research have been: The visual and photographic observation of planets and satellites; the fifth satellite of Jupiter was discovered here by Barnard in 1892. A systematic search for comets has been kept up and 14 unexpected comets have been discov ered— Barnard (3), Perrine (9), Coddington (I), besides a comet discovered by Schaeberle during his observations of the solar eclipse in Chile. Many periodic comets have also been detected and observed. The orbits of new comets have always been promptly computed at the observatory and ephemerides sent out to other stations. Four asteroids were discovered by Coddington in 1898-99. Meteors have been observed and photographed, and their orbits calculated. Double stars have been assiduously observed and many new discoveries made by Burnham, Hussey and Aitken; the orbits of a considerable number of binaries have been cal culated. Observations of the zodiacal light and of the aurora have been made by Barnard and others. Successful expeditions have been sent to observe all total solar eclipses since 1888, and very much has been added to our knowledge of solar physics in this way. The transit of Venus of 1882 and three transits of Mercury have been observed and photographed here. The posi tions of a large number of fixed stars have been determined with great precision by Tucker. Many photographs of the sun and moon have been made. The negatives of the moon have been utilized in the preparation of an atlas of the moon (scale 10 feet to the moon's diam eter) by Professor Weinek, and on a scale of three feet by Messrs. Holden and Colton. A great number of important photographs of the milky way were made here by Professor Barnard and others, and of comets and nebulae by Keeler, Hussey, Perrine and others. A com
plete outfit of seismometers for recording the intensity of earthquake shocks was installed at the observatory in and it was supple mented by similar instruments at Berkeley and at other points in California and Nevada, which regularly report to Mount Hamilton. In this way the elements for seismometric record for the State were collected and regularly pub lished. At the same time a list of all recorded shocks on the Pacific coast since 1769 was compiled and discussed by Dr. Holden. Spec troscopic observations of nebulae, new stars, comets, stars and planets have been made in great number and with previously unattainee precision by Messrs. Keeler, Campbell, Wright, Perrine and others.
The chief problem of the great telescope is to determine the motion of the solar system by spectroscopic observations. The photography of stellar spectra was proposed in the plan of 1874 and attacked in 1888, and it has been followed with marked success, especially in the hands of Professor Campbell. Since 1896 more than 2,000 negatives of stellar spectra have been secured. A preliminary discussion by Camp bell leads to the result that the solar system is moving toward a point in R. A. and 20° N. D., at a speed of 19.89 kilometers (12.35 miles) per second. An expedition was sent (at the expense of D. 0. Mills) to the southern hemisphere in 1903 to extend this research to southern stars.
The observatory publishes a series of octavo