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M.-P.-VOL. I.l DAVIDSON— APPARENT PROJECTION, ETC. 69 



the cold ocean air sweeping through the Karquinez Strait 

 added ten-fold confusion, the heliotrope image from Mt. 

 Diablo, distant forty-five miles, was seen in the telescope 

 like the waving flame from the stack of a smelting furnace. 

 Sometimes the image exceeded sixty seconds in irregular 

 diameter, and its horizontal direction was very abnormal. 

 This condition lasted for many days. When the air became 

 of more uniform temperature the image was small, star- 

 like, and steady, and its direction normal. 



In the remarkably quiet atmosphere of the mountains, 

 before sunset, with a pure sky for a background, we once 

 saw, with the two and one-eighth inches objective of the 

 theodolite, the observer leave his station, which was thirty- 

 three miles distant from Mt. Tamalpais. With a salmon- 

 colored sky in the west, and the atmosphere remarkably clear 

 and steady, Superintendent Bache observed upon the signal- 

 pole of Mt. Wachusett, distant sixty-one miles. The image 

 was nearly as dark and sharp as the cross-threads. 



In winter, at great elevation, we once saw, with a three- 

 inch objective, just after sunrise, with a serene atmosphere, 

 the heliotroper projected against a snow background at a 

 distance of fifty-one miles. From Mt. Diablo, 3,849 feet 

 elevation, with the same size objective, just before sunrise, 

 in a perfectly quiet atmosphere, when the crest-line of the 

 Sierra Nevada was projected like a dark-blue saw against 

 the warm eastern sky, and apparently only thirty or forty 

 miles distant, we saw upon several mornings the observing 

 hut on the pinnacle of Mt. Conness. The hut was six feet 

 wide by seven and a half feet high, and the distance one 

 hundred and forty-three miles ; the width therefore sub- 

 tended i".64. After the hut had been cut down to about 

 four feet we still made it out upon an extraordinarily clear 

 and steady morning. On account of the distance and great 

 height of Mt. Conness (12,566 feet) the Sun rose to the 

 heliotroper about eight minutes earlier than to Mt. Diablo. 

 The sharpness and steadiness of Mt. Conness were supreme, 

 and the image of the heliotrope was like a minute star; but 

 so soon as the Sun's rays struck the eastern flank of Mt. 



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