72 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



Davidson, who was, so to speak, at the western end of the arc of the 39th 

 parallel, which extends 2,825 miles from the Atlantic Coast, entered upon his new 

 duties with renewed vigor. Observation lines of triangulations used by him 

 reached the length of almost 200 miles — a feat at that time "unique in the history 

 of geodesy," as the Superintendent of the Coast and Geodetic Survey approvingly 

 stated. 



The crowning achievement of Davidson's career was the measurement of the 

 two base lines upon which the triangulation of California rests. In 1881 he meas- 

 ured the Yolo Base Line twice, with the result that the probable error, as com- 

 puted by his collaborator C. A. Schott, was 9.57 millimeters on a line measuring 

 17,486.5 meters — a minimum of error probably never equaled under similar cir- 

 cumstances. The story of this unusual feat may be found in the U. S. Coast and 

 Geodetic Survey Reports of 1882 and 1883. In 1888-1889 Davidson repeated this 

 performance by measuring the Los Angeles Base Line three times. 



The final achievement of the Coast and Geodetic Survey during Davidson's 

 incumbency was the definite establishment of the California-Nevada boundary. 

 California's boundaries with Oregon and Mexico had been established without 

 difficulty, though not without error. The Nevada line remained for several decades 

 a problem. Captain Sitgreaves began the survey in 1852, G. H. Goddard con- 

 tinued it in 1855, J. F. Haughton ran the line from Lake Tahoe to a point east 

 of Mono Lake in 1863, and James Lawson extended it to beyond AVhite Moun- 

 tain. In 1872-1873, San Francisco's pioneer engineer, A. W. von Schmidt, finally 

 ran through the entire line. After the Coast Survey had been placed in charge 

 of the inland triangulation, an error was discovered in checking the initial start- 

 ing point at Lake Tahoe. In the final survey, begun in 1893, von Schmidt's line 

 south of Lake Tahoe was moved west several miles. 



The total solar eclipse of January 1, 1889, helped to augment the interests of 

 Californians in astronomy. About six scientifically equipped parties and numer- 

 ous amateurs observed the phenomenon. The Astronomical Society of the Pacific 

 was organized the same year. Well supported, it soon became one of the strongest 

 organizations devoted to science. 



In 1894 the second mountain observatory was erected north of Pasadena on 

 Echo Mountain, a shoulder of Mount Lowe, at an elevation of about 2,500 feet. 

 The telescope was a 16-inch refractor, with which Lewis Swift, its owner, had 

 discovered 960 nebulae and nine comets in Rochester, New York. During the 

 next six years, as director of the Mount Lowe Observatory, Swift discovered 230 

 additional nebulae and five other comets. 



The third observatory to be established on a California mountain is on Mount 

 Wilson, 5,710 feet above sea level. It was upon S. P. Langley's recommendation 

 that the Carnegie Institution of Washington provided the funds for the estab- 

 lishment of this observatory. Langley, the director of the Allegheny Observatory, 

 had done extensive work in solar radiation and wished to check the influence of 

 the vapor and dust content at low altitude as compared to conditions at very 

 high altitude. "A southern latitude," he wrote to Davidson on May 30, 1881, 

 "dry climate, and above all, clear deep blue sky. Another important thing is the 

 provision of an adjacent station having great difference of altitude. All these 

 conditions seem to meet at Whitney." From July to September, 1881, Langley's 

 party, among them James Keeler, subsequently Director of the Lick Observatory, 



