70 CALIFORNIA ACADEMY OF SCIENCES. [Proc. jd Ser. 



Diablo the atmosphere around the observing station became 

 so unsteady that observations were made with difficulty and 

 little satisfaction. 



We had a similar experience at the transit of Venus, 

 Station Cerro Roblero, in New Mexico, in 1882. Before 

 sunrise the atmosphere was so serene that we could see, 

 with the five-inch equatorial, the small branches of the scant 

 scrub growth on the dark, sharp, blue crest-line of the 

 Organ Mountains, twenty miles distant. Immediately after 

 sunrise the suddenly heated air, rising up the steep slope of 

 the Cerro Roblero, just in front of the observatory, caused 

 great waves of disturbed air to obliterate the branches of 

 the brush and to exhibit the border of the Sun as a remark- 

 ably confused outline. The direction of these waves was 

 very marked. At the time of the first contact of the images 

 of Venus and the Sun the observations were made with 

 difficulty and doubt, and micrometer measures were almost 

 impracticable. The station was about 5,676 feet above the 

 sea, and 1,655 ^ eet above the Rio Grande and the Jornado 

 del Muerte. 



We have been thus prolix in order to indicate that the 

 principal disturbance exhibited in the telescope, as well as 

 to the unassisted eye, is in the immediate vicinity of the 

 observing station. At trigonometrical stations, in disturbed 

 conditions of the air, the confused and unsteady image of a 

 heliotrope will exhibit a movement of 5" to 15" of arc. The 

 observer could not see such movement if it took place 

 rapidly at the distant station. If the heliotrope image at 

 Mt. Connesswere moved bodily sideways forty-four inches, 

 the observer at Mt. Diablo would see it change only one 

 second in amplitude, supposing the movement were slow 

 and therefore capable of cognizance, instead of being very 

 rapid and not then capable of detection. This exhibition of 

 the locally disturbed atmosphere at the observing station can 

 be readily produced artificially. 



At Round Top station, in the Sierra Nevada, 10,435 feet 

 elevation, we counted forty-seven forest fires that arose on 

 the flanks of the forested mountains over which we were 



