M.-P— Vol. I.] DAVIDSON— APPARENT PROJECTION, ETC. 97 



observer informs us that the unsteadiness of the atmosphere 

 and the irregularity of the refraction apparently lengthened 

 the signal poles to a hundred feet and more ; and the tripod 

 supports were like great writhing snakes. Even upon some 

 small low island in the ocean, where the climatic conditions 

 are favorable, the atmosphere at night becomes very quiet 

 and serene. From a vessel's deck we have watched the 

 larger stars nearly reach the horizon with very little 

 twinkling. 



Recapitulation of Phenomena at Observation. 



These examples are a few of the many experiences in 

 our geodetic and astronomical observations, and in the 

 descriptive experiences of a few other observers. And yet 

 from recent publications there appear to be many observers 

 who do not understand the cause of the phenomena, and 

 who seem to think there must be something occult and 

 unexplainable. We have therefore felt constrained to 

 repeat this explanation which we have held and announced 

 for many years. It seems to cover every phase of the 

 phenomena. 



In the occultation of stars by the Moon, a spurious and 

 factitious limb of the Moon can be formed only and solely 

 by the unsteadiness of our atmosphere more immediately 

 surrounding the station of the observer. 



In a serene atmosphere, the outline of the Moon is so 

 sharp and clear-cut that the mountains and valleys thereon 

 are very distinctively exhibited, and will bear the largest 

 magnifying power. When the atmosphere begins to change 

 to unsteadiness, the sharp outline of the Moon (or other 

 object) is first affected by tremors or shiverings, which are 

 so infrequent that the observer is able to select the actual 

 border and its features. As the unsteadiness of the atmos- 

 phere increases, the tremors increase in frequency and in 

 amplitude, until the border of the Moon becomes a con- 

 fused, blurred outline, in which no serrations can be 

 detected. The early shiverings usually denote the direction 

 of movement of the disturbed air. Under the atmospheric 



