66 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



were made in perhaps the worst locality possible. The 

 peninsula of San Francisco near the Golden Gate is unique 

 for general unsteadiness of the atmosphere, yet marked on 

 rare occasions by some supreme exhibitions of quietness. 



Geodetic Observations in the Sierra Nevada. 



In the high Sierras of eastern California, from 7,250 to 

 10,430 feet elevation, after a great southeast storm with 

 clearing weather in the night, a strong wind from the north- 

 west, and a wonderfully pellucid sky and steady atmosphere 

 to windward that gave astonishing clearness, sharpness, 

 steadiness and apparent nearness to all objects, we have, at 

 the greater elevation, seen star-like heliotrope images with 

 the naked eye, at stations 120, 130, 140 and 160 miles 

 distant to the west and northwest, whence the cold, keen 

 wind was blowing. At this station, with the whole range 

 covered with snow, the mountain face was precipitous for 

 1,356 feet to the north. To the southeastward and east- 

 ward, over the very deep valley of the Mokelumne River, 

 directly under us, subject to the Sun's early warmth, the 

 atmosphere became excessively disturbed and the heliotrope 

 images in that direction were not visible to the eye at dis- 

 tances of forty miles. In the telescope the former images 

 were steady, round, and so minute that the micrometer 

 thread nearly covered them; the latter images were very 

 diffuse, irregular and unsteady, and ranged from twenty 

 seconds to thirty seconds in diameter. In the first case the 

 pointing was quickly and satisfactorily made; in the second 

 the pointings were unsatisfactory, even with half a dozen 

 occular pointings as checks. 



Visibility of Jupiter's Satellites. 



In astronomical work we have observed the Sun, Moon, 

 planets and stars when the Sun was serenely steady; and 

 at night not a star twinkled to the naked eye, and no irra- 

 diation was visible to Jupiter. Half a dozen times in our 

 experience we have been able to distinguish with the naked 



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