Page:Popular Science Monthly Volume 58.djvu/95

Rh the Allegheny Observatory, affording most efficient help to Professor Langley in his classical researches on the lunar heat and on the infrared portion of the solar spectrum.

Early in 1886, on Professor Holden's recommendation, Keeler was appointed assistant to the Lick trustees. He arrived at Mt. Hamilton on April 25, 1886, and immediately proceeded to establish the time service. The telegraph line to San José was perfected, the transit instrument, the clocks and the sending and receiving apparatus at both ends of the line were installed. The signals were sent out on and after January 1, 1887, north to Portland, east to Ogden and south to San Diego and El Paso. In addition to the time service, he assisted the trustees in installing the various instruments.

When the observatory was completed and transferred to the regents of the University of California, on June 1, 1888, Mr. Keeler was appointed astronomer: the original staff consisting of Astronomers Holden, Burnham, Schaeberle, Keeler and Barnard, and Assistant Astronomer Hill.

Professor Keeler was placed in charge of the spectroscopic work of the observatory. The large star spectroscope, constructed mainly from his designs, has no superior for visual observations. Of the many results obtained with this instrument we may mention the observations of Saturn's rings and Uranus, with reference to their atmospheres; of the bright and dark lines in the spectra of γ Cassiopeiæ and β Lyræ; of the color curve of the 36-inch equatorial, and of the spectra of the Orion Nebula and thirteen planetary nebulæ.

His beautiful observations on the velocities in the line of sight of these fourteen nebula? mark a distinct epoch in visual spectroscopy. His memoir on the subject took its place as a classic at once. The probable error of the final result for each nebula, based on the mean of several observations, is only 3.2 kilometers per second. Attention should be called to one extremely important fact established by these measures, viz., the velocities of the nebulae in their motion through space are of the same order of magnitude as the velocities of the stars.

The recognition of the fact that a great refracting telescope is also a most powerful spectroscope for special classes of objects, by virtue of the chromatic aberration of the objective, is due to Professor Keeler. Among the first objects observed with the 36-inch equatorial were the planetary nebula? and their stellar nuclei. The observers were struck with the fact that the focal length for a nebula is 0.4 inch longer than for its stellar nucleus; a discrepancy which Professor Keeler at once explained by recalling that the star's light is yellow, whereas that of the nebula is greenish-blue.

Astronomical readers will remember Keeler's splendid drawings of the planets Saturn, Jupiter and Mars, made with the assistance of the